Hi all
the problem you 're describing when you want to shutdown, restart or log off, appeared to me also, from the first mageia beta 1 installation until now. It shows in the background, usually, the last application that I was using and then closed, distorted, rippled, cut in pieces. Funny thing: once or twice, my Mandriva 2010.2 desktop image appeared in the background (Mandriva is installed in another physical hard disk)
Any way, the problem you mentioned, appeared while I was using the nouveau drivers (as they were present by default after the installation). After installing the nvidia proprietary drivers, the problem disappeared (but then -almost- the same problem appeared when trying to resize the konsole window, while having kwin effects enabled. It is discussed in a couple of posts elsewhere in the forum).
So, if you have nvidia graphics card and you are using the nouveau drivers, installing the proprietary nvidia drivers (from mageia repos, control center) that should fix the problem.
If you already have found another solution, please, let me know, I would like to try it.
Bye
John