Combobox Selection Problem (Dropdown Menu autohiding)

[Ltty]

I am using a FormPanel and inside I just placed the source code from the demo application for simple forms. The form panel in my application is collapsible and lies in the center of a boarder layout which is part of a layout container. Whenever I click on the expand button for my combo box, nothing happens although there are values in the combo box. I deployed it to the app engine and checked what happens. Basically the drop down box seems to appear for a very short period of time. In Firefox it pops up, but as soon as I move the curser the drop down is closed again.

I wasn't able to find a solution so far. Can anybody help me?

[Ltty]

If someone wants to see what is happening, please go to http://andruid-fhhgb.appspot.com and sign in as test@test.com. Password is test. Click on the left symbol in the project table to start the visualization view. There I integrated the example from the FormPanel demo.