They do get hot, but shouldn't get that hot.
I use AF injectors on mine in the lab (dsine). They seem ok (but the lab is quite cool).
It might be worth logging it with TAC?
I suppose there's a possibility the PoE negotiation isn't going quite right, and the switch is delivering more wattage than the AP expects.
I can't remember the HP commands, but if you compare the PoE delivery on the AP to that (show ap debug system-status ap-name NAME) see if something jumps out?