I looked into the log file (excellent idea!) and found the following:
Code:
(EE) RADEON(0): [dri] RADEONDRIGetVersion failed because of a version mismatch.
[dri] radeon kernel module version is 2.0.0 but version 1.17.0 or newer is needed.
[dri] Disabling DRI
Thus, I immediately remembered that I turned on radeon.modeset (since I ran over the post that it just works) and forgot to turn it off.
However, the error message states that 2.0.0 is not newer than 1.17.0. Is it really so or does the kernel fail to compare strings?