Related bugreport :
https://sourceforge.net/tracker/?func=detail&aid=3485712&group_id=157793&atid=805242taken from mansion_poolhouse
If the actor walks down the stair he seems to fall through it and gets stuck. If I remove the door from the map everything is fine.
I had the same problem at an early stage of this map and also on mansion_main, wich I solved be moving the doors. From this experience to me it looks like this happens, if the actor is able to 'use' the door from there (from the place where he gets stuck).
This was first reported from 'accumulator' on irc using ubuntu/amd64/ufoai-git-master, opposed to my winXP.
I added the example .map file from the picture, taken out of mansion_poolhouse.map.
This might be related :
http://ufoai.ninex.info/forum/index.php/topic,6373.msg50457.html#msg50457