This is a tricky one to describe. Accented characters that require pressing two keys ( ^ => e => ê) don't work. Pressing the accent key leaves the cursor in the same place, and pressing the letter key afterward doesn't display anything either. Once the combination is over, typing is as usual until it's time to enter another accent.
Right now all I know is that toggling fullscreen mode disables the accent preview that appears before hitting the letter. I have no clue what makes it output nothing after that.
After toggling full-screen (this is then persistent even when changing screen modes):
After ???? happens, and until the app is closed and restarted:
I've experienced it in builds 2088-2089 at least, on OS X Snow Leopard.