In the Deep-Dweller ambush one of the skeleton warriors even used Battering Ram against somebody with high-advantage, making him run through the air. He fell afterwards back to the ground because he could not get a foot on the high ground.
With attacks of Opportunity we had never problems, mainly because we only use it, if we know for sure, we get them knocked down, tough. But attacks of oppurtunity if you approach an enemie is a new add or a bug, not sure. Can be pretty annoying.