This bug appears several times on my system.
I've found a way to reproduce it.
I download a pdf in firefox with pdf download extension. The pdf opens, and then the window captions are gone. compiz still running.
Now, I switch compiz out, and they are back. Switch compiz on, everything is fine. Now, the downloads window of firefox is a few pixels size (well, possibly zero, the thing that I see is the decoration).
Clicking its button a few times on the panel crashes gtk-window-decorator. Again and again.
If I resize this window, before the crash happens (I just don't click on it's button that much), I see an empty window. I can close it without problem.