[Striiker]

I noticed a similar issue last night while fighting at the undead ruins in Qeynos Hills. My pet was not sitting down repeatedly, he was doing just fine. The Dread Corpses and Putrid Skeletons were exhibiting this behavior. It was weird, my pet was slashing away and the mob would keep sitting into a pile of bones and then pop back up again. This was observed AFTER the server reset at around 10 pm Eastern.
I should note though that not all skeleton type mobs were doing this, only a few of them. Decaying skeletons for example were fine. Some of the Putrid skeletons also appeared to be okay throughout the battle.