I also had some weird issues with 14.12.

On one machine, GPU0 would not accept GPU engine clock changes very easily. If doing it manually inside GPU settings, usually sgminer would say "driver reported failure" and the clocks would be pretty much random after that, usually very low clocks though. However, after lots and lots of tries, it actually accepted the clock change and would then run many days without problem.

This was also the same with aticonfig, also it would report fail and GPU0 would have random clocks afterwards.

gpu-auto in sgminer didn't really work at all, because it would get stuck at some low frequency if the clock setting failed. I did a small patch, that would retry increasing the clock after a few seconds, until full speed is reached.. But it could take something like 30 minutes to get it running at full clocks!

All this was only on GPU0, other GPUs were fine. I didn't try switching boards around, but with 14.6 drivers GPU0 changes clocks without problems.

On my other machine, 14.12 would crash X instantly if starting sgminer. This was fixed with option --no-adl. I remember having exact same behaviour with some Catalyst 13.xx, it didn't like "fanless" GPUs where GPU fan readings are always at 0rpm.. This is a watercooled system so there are no fans.  However 14.6 again works fine, with adl enabled.

So now I'm back at 14.6. I have a desktop machine with 14.12, and run CodeXL there so I can generate 14.12 binaries for any GPU.. They usually work just fine with 14.6 drivers.