Downgrading xorg-server to 1.2.0-r3 and then restarting the xdm service on kelpie seems to’ve done the trick. Admittedly I’m sitting at the other end of a ssh connection, which may be prejudicing my view, but the current Xorg.93.log seems to bear me out. It’s fallen back to software rendering due to an ABI incompatibility with the current fglrx, but that’s alright.