Broke Charm, Mob Instantly Regained Full HP
 

Casted invis to break charm on "a drolvarg snarler" in FV when the mob was below 10% HP, and when charm broke, the mob instantly had 100% HP. He was engaged with another snarler. The mob may have had a killing blow at the same time charm broke.

Never had this happen before.

Resolving for lack of evidence / repeatability, could have been someone passing by and healing pet right before charm break.