After resurrecting a dead pet all features it has got once by feeding are gone!
Although it still looks like an 'adult' pet with aura, it only has now the basic attributes like a 'baby' pet.
You easily can check it out - just take a pet to the Kaderak mines in act 3 and let it hit a powder barrel (i hope there is one left at least...
)
The full pet attributes get re-initiated if you send the pet to the inn and get it back again, or if you restart the game.
I only have (temporarly) sacrified my ice-elemental pet and my dire wolf, but i supposed this may be a gerneral bug!? - I have found nothihng about it...