Error from Vaadin using Virtual Servers from Tomcat

I have deployed a Vaadin application called for example myApp under Apache Tomcat and used Tomcat Web Server to create a Virtual Server and use a friendly domain called myDomain for example. The configuration of the virtual server on Apache Web Server is:

<Virtualhost *:80>
ServerAlias myApp

    ErrorLog /var/log/apache2/myDomain.com_error.log
    LogLevel warn
    CustomLog /var/log/apache2/myDomain.com_access.log combined

    # Proxy to Tomcat
    <Proxy *>
            Order deny,allow
            Allow from all

    ProxyRequests On
    ProxyPass /myApp/VAADIN/ http://myIP:8080/myApp/VAADIN/
    ProxyPassReverse /myApp/VAADIN/ http://myIP:8080/myApp/VAADIN/
    ProxyPass /myApp/APP/ http://myIP:8080/myApp/APP/
    ProxyPassReverse /myApp/APP/ http://myIP:8080/myApp/APP/
    ProxyPass / http://myIP:8080/myApp/
    ProxyPassReverse / http://myIP:8080/myApp/

    <Location />
            Order allow,deny
            Allow from all

If I connect thorugh this uri everything is ok, the Vaadin web App runs and navigate corretly. But the problem exist when I show a print view in a _blank new page, before show it, if click in any part of the page I obtained a red error from Vaadin with a ‘Communitacion problem’

However if connect to the Web App from this uri http://myIP:8080/myApp (not using the firndly domain) the problem NOT exist;(

What is the problem?, is from Tomcat or from Vaadin?