Not sure I have ever run into that problem. It may happen if there is already one there and you try to buff it, but if you buff it first I don't think it will over-write it and then disappear afterwards.
Then again, what warlocks use a felhunter (at least in raids)? Or are you talking about PvP or something?
If you are lower level then the lock, this will happen. The lock probably is higher level and has the higher fel intelligence spell learned, once you get to 80, yours will not go away.
If you are lower level then the lock, this will happen. The lock probably is higher level and has the higher fel intelligence spell learned, once you get to 80, yours will not go away.
This. AI/AB at max level offers a higher Int buff and as such is prioritized. Divine Spirit is the same way with regards to Fel Intelligence.