It seems, like it's not possible to use a VBoxLayoutContainer within a TabPanel:
public void onModuleLoad()
TabPanel tab = new TabPanel();
//ContentPanel f = new ContentPanel(); // --> this one works great
VBoxLayoutContainer f = new VBoxLayoutContainer();
tab.add(new TextButton("testButton"), "showTestButton");
And that's, how it looks like: bug-tabpanel.jpg
The Label (or any other Widget) is rendered over the whole TabPanel. A ContentPanel doesn't make such problems, but since I am using VBoxLayoutContainer most of the time (automatic strech and flex on last item is just great), I hope this one will get fixed.
It seems like the GWT-TabPanel has the same behaviour. It work's fine with a GWT-TabLayoutPanel , but since I prefer the GXT widget, I have to use a ContentPanel wrapper to show my VBoxContainer correctly.
I had no problems with GXT 2.x - but since you're obviously trying to close the gap between GXT and GWT, equal behaviour is the right way to go. My solution shouldn't stay unmentioned though, since I don't think I'm the last person facing this problem.