Version: (using KDE 4.2.0) OS: Linux Installed from: Gentoo Packages The easiest way to reproduce is: 1. open konsole 2. run some windowed app, kwrite for example 3. hit ^Z to stop the process. now it wouldn't respond 4. press the X (close) key on the kwrite's window frame 5. after some time standard dialog appears asking whether we want to kill non responsing app or wait for more. Asking to kill. 6. After that the whole desktop freezes completely for around 10 seconds, then it gets back to normal.
All of this strange effects are caused by infamous nvidia-drivers-180.35 bug. Downgrading the drivers fixed the whole thing. For more information, visit: http://bugs.gentoo.org/show_bug.cgi?id=260441