That previous link might be helpful, assuming radeon is having the same problem has radeonhd. It's also possible that updating either driver won't solve the problem, I really don't know.
Updating the radeonhd driver, however, is the simplest option, and it's what I'd recommend first. If it doesn't work, you could try the steps in that other thread I linked to. Essentially, you'll want to follow these steps:
wget
ftp://ftp.x.org/pub/individual/drive...d-1.3.0.tar.gz
tar xzvf xf86-video-radeonhd-1.3.0.tar.gz
cd xf86-video-radeonhd-1.3.0
./configure --with-xorg-module-dir=/usr/lib/xorg/modules/
make
make install
That last step you will need to do as root (or with sudo).
That will update you to the most recent release of the radeonhd driver. I've tested those steps on a stock slackware 13.0 32-bit installation, and it worked just fine.
Adam