OpenGL acceleration glitch (only on dapper 64)

Binary package hint: xserver-xorg-driver-ati

Ok I'm pretty sure this is a software issue.

Running on dapper amd64 with a radeon 9250 (from tungsten, same problem occurred with the ati 9200 card, which works normally on another machine under dapper32)

Apps using opengl acceleration work, but if the window loses focus. The image splits in 1/2, and seems to draw only on the left edge of the screen. Going to fullscreen and back solves it. Problem is easily reproducable, and gives no sort of error output when it occurs (AFAIK).

Here are some example screenshots (occurs with other apps that use opengl too, like glxgears, flightgear, dosbox (if it's set to use opengl) etc.:

Normal.

http://img48.imageshack.us/img48/4564/screenshotx10jq.png

After clicking somewhere else.
you can see it's split in half and duplicated
http://img48.imageshack.us/my.php?image=screenshotx23to.png

Here you can see moving the window around. Only the left part is drawn, rest shows some sort of garbage.
http://img135.imageshack.us/my.php?image=screenshotx35cc.png

These last 2 illustrate where changes are being drawn
http://img74.imageshack.us/my.php?image=screenshotx45ez.png
http://img386.imageshack.us/my.php?image=screenshotx55hd.png

Then it's normal after going to fullscreen and back.

The warnings when running an opengl app:
 glxgears
libGL warning: 3D driver claims to not support visual 0x23
libGL warning: 3D driver claims to not support visual 0x24
libGL warning: 3D driver claims to not support visual 0x25
libGL warning: 3D driver claims to not support visual 0x26
libGL warning: 3D driver claims to not support visual 0x27
libGL warning: 3D driver claims to not support visual 0x28
libGL warning: 3D driver claims to not support visual 0x29
libGL warning: 3D driver claims to not support visual 0x2a
libGL warning: 3D driver claims to not support visual 0x2b
libGL warning: 3D driver claims to not support visual 0x2c
libGL warning: 3D driver claims to not support visual 0x2d
libGL warning: 3D driver claims to not support visual 0x2e
libGL warning: 3D driver claims to not support visual 0x2f
libGL warning: 3D driver claims to not support visual 0x30
libGL warning: 3D driver claims to not support visual 0x31
libGL warning: 3D driver claims to not support visual 0x32

I'm not sure if there is a connection...

Any suggestions/fixes would be appreciated. :)