blender screen problem when desktop-effetct is activated (feisty)

Hi,

I use the free ati drivers. I have no problem with them. All is OK, Compiz works perfectly.
I have this problem only with blender

when I load blender in a console, I have this message:

"thomas@thor-ubuntu\IP=[]:~$ blender
guessing 'blender-bin' == '/usr/bin/blender-bin'
Compiled with Python version 2.4.
Checking for installed Python... got it!
Ignoring Xlib error: error code 169 request code 145
Ignoring Xlib error: error code 169 request code 145
*********************************WARN_ONCE*********************************
File r300_render.c function r300Fallback line 428
Software fallback:ctx->Line.SmoothFlag
***************************************************************************
Try R300_SPAN_DISABLE_LOCKING env var if this hangs.
*********************************WARN_ONCE*********************************
File r300_render.c function r300Fallback line 426
Software fallback:ctx->Line.StippleFlag
***************************************************************************
*********************************WARN_ONCE*********************************
File r300_vertexprog.c function valid_dst line 333
Output 13 not used by fragment program
***************************************************************************

Blender quit"

I can't explain which is exactly the problem but look at this screenshoot.
http://img219.imageshack.us/my.php?image=affichageblendertc8.png