If I put my pet on assist, it sometimes returns to me for apparently no reason (as if I had called him back). After a short break, he runs to my target again.
Normally I don't mind this too much, but yesterday at the trash mobs before Lei Shen, I noticed my pet (I think it was my arcane wyrm serpent or the tallstrider) doing it constantly:
attack once, run back to me. attack once more, come back to me etc.
I thought: "maybe the pet automatically returns while their lightning shield is active", but I was careful not to damage a mob with a shield, and it happened nevertheless. I also made sure that it's not returning because I have a /petfollow in a macro somewhere by only using autoattacks... still my pet was running back and forth like rabid.
So, what gives? I don't particularly care about 4 trash mobs, but randomly losing pet uptime on bosses might get a bit annoying.
I also encountered this problem during the Dark Heart of Pandaria scenario. I commanded my cat to attack the oozes that dwell in the cave, and he also leaped back and forth like he was using Rabid.
I had my pet on Passive all the time, but I don't think that has anything to do with this minor bug. While doing the Battlefield: Barrens quest, after the scenario, I didn't encounter the bug anymore.
I haven't noticed this at all. Having pet on assist is generally advised against in a raid because it will cause it to run around being stupid whenever you change target. Personally I leave my pet on passive and macro /petattack into my Arcane Shot.