I too am having the half screen issue, changing browsers doesn't help and clearing cache didn't do anything either. The same issue was happening in other games but one of those games has done a fix I'm hoping you can do, it now has a vertical/horizontal scroll bar at right/bottom of the app and works. Just a thought that perhaps you hadn't considered it, since obviously FB doesn't seem to care how much they screw us over.
Check out this thread for information about how we have pushed a temp fix until Facebook can fix this issue :http://forums.kanoapps.com/showthread.php?t=4004&page=6
