Vaadin 7: SubWindow and Scrollable Problem

Hi, i cant get the SubWindow Scrollable.
I already read the doc, but cant fix this.

Here is my code:
The grid is dynamically filled with images

public class FileBrowserWindow extends Window {
private final ApplicationUI ui = (ApplicationUI) UI.getCurrent();
private GridLayout grid;
private Button uploadButton;
private Button cancelButton;
private String seletedItemPath;

public FileBrowserWindow() {
setWidth(800, Unit.PIXELS);
setHeight(600, Unit.PIXELS);
setResizable(false);
setClosable(false);
setCaption(ui.getLocalizedText("filebrowser.window.titel"));
layout();
}

private void layout() {

VerticalLayout content = new VerticalLayout();

content.addStyleName("subWindowContent");
content.setSizeUndefined();

HorizontalLayout buttonWrapper = new HorizontalLayout();
buttonWrapper.setHeight(40,Unit.PIXELS);
uploadButton = new Button("Datei hochladen");
cancelButton = new Button("Abbrechen");

buttonWrapper.addComponent(uploadButton);
buttonWrapper.addComponent(cancelButton);

content.addComponent(buttonWrapper);

grid = new GridLayout();
grid.setSpacing(true);
grid.setMargin(true);
grid.setColumns(4);
grid.setDefaultComponentAlignment(Alignment.MIDDLE_CENTER);
grid.setImmediate(true);

content.addComponent(grid);
setContent(content);

}

public void updateContent(List<File> availableFiles) {
for(File file : availableFiles){
FileResource resource = new FileResource(file);
Image image = new Image(file.getName(),resource);
image.setHeight(150,Unit.PIXELS);
image.setWidth(150,Unit.PIXELS);
image.addClickListener(new MouseEvents.ClickListener() {
@Override public void click(MouseEvents.ClickEvent event)
{ Image component = (Image)event.getSource();
FileResource resource = (FileResource) component.getSource();
seletedItemPath =resource.getSourceFile().getPath(); close(); } });
getGrid().addComponent(image); } }

...

In the generated HTML the div  has css with overflow hidden instead of auto

<div tabindex="0" class="v-scrollable" style="zoom: 1; position: relative;">

window-contents > .v-scrollable {
padding: 0;
overflow: hidden;
}

What do I need to change in Java to change this ?