I've found the Catalyst RandR 1.2 support to be quite buggy. Most of the issues I've encountered seem to only show up when using two monitors.
For example, the following sequence of commands crashes the X server (backtrace leading to fglrx_drv.so):
or, with only a single monitor:
xrandr --output CRT1 --mode 1280x1024
xrandr --output CRT2 --mode 1280x1024 --right-of CRT1
xrandr --output CRT1 --off
A second issue is creating a fullscreen window on the second monitor ends up displaying the contents on the first monitor (first monitor at 0,0 offset). The actual window is on the second monitor as it is necessary to click there for the actual mouse clicks to be recognized. This does not happen if Xinerama is used instead.
xrandr --output CRT1 --crtc 1 --mode 1280x1024
And then there are other issues that I've encountered programming using libXrandr. For example, in some configurations (this one I haven't reproduced, but have had reports of it affecting multiple users), it looks like setting a configuration, and then setting the same configuration again later will result in an X error being thrown, crashing the program. New randr info about the configuration was fetched between, so it is not trying to set using outdated info.
Have others encountered similar issues? If so, are you aware of configuration changes/workarounds for them?