Black instead of transparent in nikki (qt 4.7.4 + xf86-video-ati-git 20111215)

Hi, I'm on an arch linux 64bit system and running the game Nikki and the Robots (uses qt 4.7.4 for drawing) looks like this:

http://i.imgur.com/2HW1c.png

The black boxes around the letters are supposed to be transparent.

This also happens with xf86-video-ati 6.14.3 from the official arch extra/ repo. This does not happen when using catalyst.

Can anybody reproduce this? Does anybody have an idea what the reason might be, how to find out the reason or how to fix this?

FYI:

Code:

$ cat /etc/X11/xorg.conf.d/20-radeon.conf Section "Device" Identifier "Radeon" Option "ColorTiling" "on" Option "AccelMethod" "EXA" Option "EnablePageFlip" "on" Option "EXAVSync" "yes" EndSection

Feh also displays images with black background, even though they have transparent bg.
Gimp, gwenview, rox-filer and GQview display pngs with transparent bg correctly (chessboard bg).