Yeauhup, my Afterburner went voltage locked on my Sapphires as well. I think our cards were locked from launch. I could be wrong though cause I got mine used. But my 5770 worked just fine unlocked in AB. Only when I upgraded did AB voltage control disappear from their control panel.
Now it could be that updating the Sapphire software pack could rectify there issue. Mine aren't online so I haven't been able to test this for myself.