I ran into one of those for the first time with my MP yesterday.
My pets refused to follow me out of the main room (up the 'tongue' and through the door).
After several minutes of running back, hitting 'follow' and walking slowly into the next room (only to see them start moving, then stop and go back to sulk in the corner), I gave up and killed them all.
=(
Side note:
Pets sometimes seem to have problems targeting if they are on a hillside and the mob is above/below them.