One possible answer to my own question is, that AMD's ATI Catalyst driver disables the Xorg RandR extension and enables it's own RandR extention:
from /var/log/Xorg.0.log:
[...]
[ 68.714] (II) fglrx(0): RandR 1.2 support is enabled!
[ 68.714] (II) fglrx(0): RandR 1.2 rotation support is enabled!
[...]
[ 69.541] (II) fglrx(0): Disabling in-server RandR and enabling in-driver RandR 1.2.
[ 69.975] (--) RandR disabled
[...]
[ 69.975] (II) Initializing built-in extension RANDR
[...]
[ 92.101] (II) fglrx(0): Restoring Recent Mode via PCS is not supported in RANDR 1.2 capable environments
One possible answer to my own question is, that AMD's ATI Catalyst driver disables the Xorg RandR extension and enables it's own RandR extention:
from /var/log/ Xorg.0. log:
[...]
[ 68.714] (II) fglrx(0): RandR 1.2 support is enabled!
[ 68.714] (II) fglrx(0): RandR 1.2 rotation support is enabled!
[...]
[ 69.541] (II) fglrx(0): Disabling in-server RandR and enabling in-driver RandR 1.2.
[ 69.975] (--) RandR disabled
[...]
[ 69.975] (II) Initializing built-in extension RANDR
[...]
[ 92.101] (II) fglrx(0): Restoring Recent Mode via PCS is not supported in RANDR 1.2 capable environments
Any idea, how to change this configuration?