Created attachment 64140 [details]
example of a black dialog

Version:           unspecified (using KDE 4.7.1) 
OS:                Linux

When desktop effects in KDE (plasma) are on, it can happens that the content of
the window goes black. The window decoration is normal, just the content is
black. It happens randomly and not allways with the same application. For
example, you can open twice the same dialog, it will not allways happen.
If you reduce the size of the window, it can solve the problem.

Disabling desktop effects Alt+Shift+F12 solves the problem but there is no more
effects.

My graphic card: Nvidia GeForce 6200SE TurboCache(TM)
My driver: NVIDIA 275.21

My version of KDE is 4.7.1 but IT HAPPENNED ALSO WITH 4.6

Reproducible: Sometimes

Steps to Reproduce:
1. Be sure the desktop effects of KDE are on
2. Open a window, a dialog or call a window from a program

Actual Results:  
The window or dialog is black.

Expected Results:  
You should see the content in the window

Workarounds
- Reduce the window size -> the content will eventually appear
- Turn off the effects (Alt+Shift+F12)

Bug also reported in openSUSE's bugzilla: https://bugzilla.novell.com/show_bug.cgi?id=720243