My setup:
- iPad 2
- iOS 5 Beta 7
- open the FCD app
- open a card deck
- click on the bottom-right icon to see the list of cards
- click on search field with magnifying glass, keyboard appears
- click on hide keyboard button, the most bottom-right button on the keyboard
- half of the screen remains empty, which is the bug
I've tried it also on my colleague's iPad 2 with iOS 4.3.5 and the bug is present there too.