Comment 61 for bug 467668

Ops... good idea, but too late.
Tony, you still got your old file?
Anyone else?

I think anyone can reproduce it, unless their system doesn't allow desktop effects.
Run a vanilla Karmic install, log in, enable desktop effects.
Boot with Lucid, log in with the same home user, enable desktop effects, log out, log in, disable desktop effects, log out, log in, enable desktop effects, log out, log in, and at some point you will have lost window borders forever.