I couldn't find release notes for the 10.12 catalyst driver online, however afaik hd4xxx and hd5xxx *should* work with the current natty setup, so this seems to be a legit bug.
However, note that in the next week or so we'll be uploading a new xserver which will completely break everything for fglrx, due to abi incompatibility. So it will be completely broken very soon regardless.
I couldn't find release notes for the 10.12 catalyst driver online, however afaik hd4xxx and hd5xxx *should* work with the current natty setup, so this seems to be a legit bug.
However, note that in the next week or so we'll be uploading a new xserver which will completely break everything for fglrx, due to abi incompatibility. So it will be completely broken very soon regardless.