a tip to help avoid having it happen to you: enter Ant Queen Lair one PC at a time, when people enter too quickly after another PC is when it seems to happen most, try waiting 7 seconds, as a heartbeat is 6, and tho im not sure if this is hearbeat related or not, it should certainly be enough time...
If its not script related (that seems right as it only happens at ant, and nowhere else) then could it be possibly be having some kind of confusion over the data used for determining the particular ant Waypoints?