Does this happen to you always, or sporadically? For me:
I get this problem intermittently. It is more than just not breaking mez. The enchanter will keep the mobs mezed since the paladin won't break it. Draining all of the enchanter's mana. Then the mobs will beat/kill the enchanter, then the next closest character. All the while none of the paladins heals go off. Kill them, then the next, until it hits the paladin and he starts working again, which usually means the paladin will chain cast gift of res in combat.
Annoying stuff how it snowballs and you lose half the team if you aren't watching to press 'tab' and turn the paladin to wake him up. For one kill, then it will stop reacting again. The paladin won't start fully working until the entire encounter finishes and his xtarget window is empty.
I'd say 2-3 time an hour at a fast camp with light blues. Not always a wipe though. if the mobs run past the paladin to get to the enchanter, the paladin will wake up & everything goes back to normal till the next time.
I think it gets stuck starting the looking for memblured mobs routine. When it is working normally, I can see it in the MQ window the looking for memblur message. When the paladin freezes up that message doesn't show up.