RPC call to v.v received for connector X but no such connector could be fou

I have this code:

package test;

import javax.annotation.Resource;
import javax.enterprise.concurrent.ManagedThreadFactory;
import javax.servlet.annotation.WebServlet;

import com.vaadin.annotations.PreserveOnRefresh;
import com.vaadin.annotations.Push;
import com.vaadin.annotations.Theme;
import com.vaadin.annotations.VaadinServletConfiguration;
import com.vaadin.annotations.Widgetset;
import com.vaadin.cdi.CDIUI;
import com.vaadin.cdi.server.VaadinCDIServlet;
import com.vaadin.server.Sizeable;
import com.vaadin.server.VaadinRequest;
import com.vaadin.ui.Alignment;
import com.vaadin.ui.Button;
import com.vaadin.ui.HorizontalLayout;
import com.vaadin.ui.Label;
import com.vaadin.ui.ProgressBar;
import com.vaadin.ui.UI;
import com.vaadin.ui.VerticalLayout;
import com.vaadin.ui.Window;

@Theme("mytheme")
@Widgetset("test.MyAppWidgetset")
@CDIUI("")
@Push
@PreserveOnRefresh
public class MyUI extends UI {

    @Resource
    private ManagedThreadFactory threadFactory;

    @Override
    protected void init(VaadinRequest vaadinRequest) {
        final VerticalLayout layout = new VerticalLayout();
        layout.setMargin(true);
        Button button = new Button("Click Me");
        button.addClickListener(
                new Button.ClickListener() {
                    @Override
                    public void buttonClick(Button.ClickEvent event) {
                        getUI().access(new Runnable() {
                            @Override
                            public void run() {
                                final Window loadingDialog = createPleaseWaitWindow();
                                getUI().addWindow(loadingDialog);
                                new Thread(new Runnable() {
                                    @Override
                                    public void run() {
                                        getUI().access(
                                            new Runnable() {
                                                @Override
                                                public void run() {
                                                    try {
                                                        Thread.sleep(2000);
                                                        layout.addComponent(new Label("Thank you for clicking"));
                                                    } catch (InterruptedException e) {
                                                        e.printStackTrace();
                                                    } finally {
                                                        getUI().removeWindow(loadingDialog);
                                                    }
                                                }
                                            }
                                        );
                                    }
                                }).start();
                            }
                        });

                    }
                }
        );
        layout.addComponent(button);
        setContent(layout);
    }


    public Window createPleaseWaitWindow() {
        Window window = new Window("Please wait...");
        window.setClosable(false);
        window.setResizable(false);
        window.setModal(true);
        window.setDraggable(false);
        window.setWidth(200, Sizeable.Unit.PIXELS);
        window.setHeight(100, Sizeable.Unit.PIXELS);

        ProgressBar progressBar = new ProgressBar();
        progressBar.setIndeterminate(true);

        HorizontalLayout loadingLayout;
        loadingLayout = new HorizontalLayout(progressBar);
        loadingLayout.setWidth(100, Sizeable.Unit.PERCENTAGE);
        loadingLayout.setComponentAlignment(progressBar, Alignment.MIDDLE_CENTER);

        window.setContent(loadingLayout);
        return window;
    }

    @WebServlet(urlPatterns = "/*", name = "MyUIServlet", asyncSupported = true)
    @VaadinServletConfiguration(ui = MyUI.class, productionMode = false)
    public static class MyUIServlet extends VaadinCDIServlet {
    }
}

POM:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>test</groupId>
    <artifactId>test</artifactId>
    <packaging>war</packaging>
    <version>1.0-SNAPSHOT</version>
    <name>test</name>

    <properties>
        <vaadin.version>7.4.5</vaadin.version>
        <vaadin.plugin.version>${vaadin.version}</vaadin.plugin.version>
        <jetty.plugin.version>9.2.3.v20140905</jetty.plugin.version>
        <project.source.version>1.7</project.source.version>
        <project.target.version>1.7</project.target.version>
        <project.encoding>UTF-8</project.encoding>
    </properties>

    <repositories>
        <repository>
            <id>vaadin-addons</id>
            <url>http://maven.vaadin.com/vaadin-addons</url>
        </repository>
        <repository>
            <id>vaadin-snapshots</id>
            <url>https://oss.sonatype.org/content/repositories/vaadin-snapshots/</url>
            <releases>
                <enabled>false</enabled>
            </releases>
            <snapshots>
                <enabled>true</enabled>
            </snapshots>
        </repository>
    </repositories>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>com.vaadin</groupId>
                <artifactId>vaadin-bom</artifactId>
                <version>${vaadin.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <dependencies>
        <dependency>
            <groupId>com.vaadin</groupId>
            <artifactId>vaadin-cdi</artifactId>
            <version>1.0.2</version>
        </dependency>
        <dependency>
            <groupId>javax.enterprise</groupId>
            <artifactId>cdi-api</artifactId>
            <version>1.2</version>
        </dependency>
        <dependency>
            <groupId>javax.annotation</groupId>
            <artifactId>javax.annotation-api</artifactId>
            <version>1.2</version>
        </dependency>
        <dependency>
            <groupId>javax</groupId>
            <artifactId>javaee-api</artifactId>
            <version>7.0</version>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.0.1</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>com.vaadin</groupId>
            <artifactId>vaadin-server</artifactId>
        </dependency>
        <dependency>
            <groupId>com.vaadin</groupId>
            <artifactId>vaadin-push</artifactId>
        </dependency>
        <dependency>
            <groupId>com.vaadin</groupId>
            <artifactId>vaadin-client</artifactId>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>org.vaadin.addon</groupId>
            <artifactId>confirmdialog</artifactId>
            <version>2.1.2</version>
        </dependency>
        <!--
          Needed when using the widgetset optimizer (custom ConnectorBundleLoaderFactory).
          
          For widgetset compilation, vaadin-client-compiler is automatically added on the
          compilation classpath by vaadin-maven-plugin so normally there is no need for an
          explicit dependency.
        -->
        <!--
        <dependency>
            <groupId>com.vaadin</groupId>
            <artifactId>vaadin-client-compiler</artifactId>
            <scope>provided</scope>
        </dependency>
        -->
        <dependency>
            <groupId>com.vaadin</groupId>
            <artifactId>vaadin-themes</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.0</version>
                <configuration>
                    <encoding>${project.encoding}</encoding>
                    <source>${project.source.version}</source>
                    <target>${project.target.version}</target>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-resources-plugin</artifactId>
                <version>2.6</version>
                <configuration>
                    <encoding>${project.encoding}</encoding>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>2.3</version>
                <configuration>
                    <failOnMissingWebXml>false</failOnMissingWebXml>
                    <!-- Exclude some unnecessary files generated by the GWT compiler. -->
                    <packagingExcludes>WEB-INF/classes/VAADIN/gwt-unitCache/**,
                        WEB-INF/classes/VAADIN/widgetsets/WEB-INF/**</packagingExcludes>
                </configuration>
            </plugin>
            <plugin>
                <groupId>com.vaadin</groupId>
                <artifactId>vaadin-maven-plugin</artifactId>
                <version>${vaadin.plugin.version}</version>
                <configuration>
                    <extraJvmArgs>-Xmx512M -Xss1024k</extraJvmArgs>
                    <webappDirectory>${basedir}/target/classes/VAADIN/widgetsets</webappDirectory>
                    <draftCompile>false</draftCompile>
                    <compileReport>false</compileReport>
                    <style>OBF</style>
                    <strict>true</strict>
                </configuration>
                <executions>
                    <execution>
                        <goals>
                            <goal>update-widgetset</goal>
                            <goal>compile</goal>
                            <!-- disabled by default to use on-the-fly theme compilation -->
                            <!-- <goal>compile-theme</goal> -->
                        </goals>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-source-plugin</artifactId>
                <version>2.4</version>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-clean-plugin</artifactId>
                <version>2.6.1</version>
                <!-- Clean up also any pre-compiled themes -->
                <configuration>
                    <filesets>
                        <fileset>
                            <directory>src/main/webapp/VAADIN/themes</directory>
                            <includes>
                                <include>**/styles.css</include>
                                <include>**/styles.scss.cache</include>
                            </includes>
                        </fileset>
                    </filesets>
                </configuration>
            </plugin>

            <!-- The Jetty plugin allows us to easily test the development build by
                running jetty:run on the command line. -->
            <plugin>
                <groupId>org.eclipse.jetty</groupId>
                <artifactId>jetty-maven-plugin</artifactId>
                <version>${jetty.plugin.version}</version>
                <configuration>
                    <scanIntervalSeconds>2</scanIntervalSeconds>
                </configuration>
            </plugin>
        </plugins>

        <pluginManagement>
            <plugins>
                <!--This plugin's configuration is used to store Eclipse m2e settings only. It has no influence on the Maven build itself.-->
                <!-- TODO Remove when http://dev.vaadin.com/ticket/14924 is resolved -->
                <plugin>
                    <groupId>org.eclipse.m2e</groupId>
                    <artifactId>lifecycle-mapping</artifactId>
                    <version>1.0.0</version>
                    <configuration>
                        <lifecycleMappingMetadata>
                            <pluginExecutions>
                                <pluginExecution>
                                    <pluginExecutionFilter>
                                        <groupId>com.vaadin</groupId>
                                        <artifactId>
                                            vaadin-maven-plugin
                                        </artifactId>
                                        <versionRange>[7.1.11,)</versionRange>
                                        <goals>
                                            <goal>resources</goal>
                                            <goal>update-widgetset</goal>
                                            <goal>compile</goal>
                                            <goal>compile-theme</goal>
                                        </goals>
                                    </pluginExecutionFilter>
                                    <action>
                                        <ignore></ignore>
                                    </action>
                                </pluginExecution>
                            </pluginExecutions>
                        </lifecycleMappingMetadata>
                    </configuration>
                </plugin>
            </plugins>
        </pluginManagement>

    </build>

</project>

After first click on button there is no problem but another clicks outputs this to console:

14:21:33,144 WARNING [com.vaadin.server.communication.ServerRpcHandler]
(default task-4) RPC call to v.v received for connector 4 but no such connector could be found. Resynchronizing client.
14:21:33,147 WARNING [com.vaadin.server.communication.ServerRpcHandler]
(default task-4) RPC call to v.v received for connector 4 but no such connector could be found. Resynchronizing client.
14:21:36,678 WARNING [com.vaadin.server.communication.ServerRpcHandler]
(default task-5) RPC call to v.v received for connector 12 but no such connector could be found. Resynchronizing client.
14:21:36,686 WARNING [com.vaadin.server.communication.ServerRpcHandler]
(default task-5) RPC call to v.v received for connector 12 but no such connector could be found. Resynchronizing client.
14:21:39,593 WARNING [com.vaadin.server.communication.ServerRpcHandler]
(default task-3) RPC call to v.v received for connector 20 but no such connector could be found. Resynchronizing client.
14:21:39,595 WARNING [com.vaadin.server.communication.ServerRpcHandler]
(default task-3) RPC call to v.v received for connector 20 but no such connector could be found. Resynchronizing client.
14:21:42,561 WARNING [com.vaadin.server.communication.ServerRpcHandler]
(default task-7) RPC call to v.v received for connector 28 but no such connector could be found. Resynchronizing client.
14:21:42,563 WARNING [com.vaadin.server.communication.ServerRpcHandler]
(default task-7) RPC call to v.v received for connector 28 but no such connector could be found. Resynchronizing client.
14:21:47,571 WARNING [com.vaadin.server.communication.ServerRpcHandler]
(default task-8) RPC call to v.v received for connector 36 but no such connector could be found. Resynchronizing client.
14:21:47,573 WARNING [com.vaadin.server.communication.ServerRpcHandler]
(default task-8) RPC call to v.v received for connector 36 but no such connector could be found. Resynchronizing client.

Should I worry about these warnings? Is my usage of threads correct?