Monsters won't teleport?

[Dewalrus]

I'm working on a mechanism that uses two-square rooms with a monster in one square and a teleporter in the other, separated by a door. When the player trips a trigger, the door opens and the monster is free to walk into the teleporter. When I tested this initially, it worked perfectly -- the monster hits the teleporter and is ported to the target location. But when I tried to put it into my actual level, which contains 15 of these teleporters, the monster's won't teleport. The rest of the mechanism works, but when the monsters walk into the teleporter, it has no effect; they can walk in and out repeatedly and go nowhere. I've checked the teleporter settings many times and they are definitely set to allow triggering by monsters. What might be going on?

[minmay]

Monsters can't teleport if something is blocking the other side, such as the party or another monster.

[Dewalrus]

There can't be a player or mob in the way, but I did mark the destination squares with an invisible, non-obstacle object -- I bet the AI thinks that's an obstacle. Will check if that solves it -- thanks!