I ran into this while in Lava last night. Using Necro undead charm Control Undeath - 55 (nice name) I had my pet up and I charm a lvl 49 heroic ^^^ mob, the pet window converted to the new mob but my pet didn't die.
So I had both pets defending me and and attacking off the standard pet controls. I then rebuffed the pet and gave them my offensive stance and saw a huge increase in preformance (however not actually parsed) when attacking other ^^^ mobs with the two.
Anyway I "assume" this is a bug as I can't imagine them allowing you to have a normal pet as well as a charmed pet at your command (charm lasts a solid 25 min. also!).
OH and using the necro wussy pet heal seemed to heal both pets at the same time.
yeah, i dont have a necro myself, but my friend has one, and ive seen him charm some bad@ss undead in the new expansion (since most of the expansion is undead =P )