Why part of the window underneath hangs on the one above

[Ariya]

Why part of the window underneath hangs on the one above after being minimized? I tried logging off, but it won't go away, only if I reboot, it would. Mostly, it is the changing gif or something, which was on the minimized window that hangs on. It becomes annoying after sometime. Even, if I refresh the desktop it won't go away.

How to get it off?

My system is Sabayon 6 KDE.

Linux sabayon 2.6.39-sabayon #1 SMP Wed Jun 15 22:52:37 UTC 2011 i686 Intel(R) Core(TM) i3 CPU M 350 @ 2.27GHz GenuineIntel GNU/Linux