Stairs building miles away from the target?!

[Memfis]

I just realized that something really freaky happens on a map I made yesterday. I have a switch that builds stairs at two points. I noticed that my monster closet breaks after I press it so I recorded a demo, watched it with walkcam and apparently the switch builds some stairs in that closet as well! Even though it isn't tagged or anything. The weird behavior goes away if I use another floor flat in that closet so it isn't really a problem but... how the hell does that happen anyway?
Here is a little illustration: http://i.imgur.com/gaF6dWp.png

[scifista42]

Check if any of the sectors are joined. The stairs effect applies through joined sectors as well.

[Memfis]

No, they aren't joined.
I just tried making a stripped version to post it here but now only one of the stairs get built (so not even all of the intended ones). I wonder if it's actually incorrect to start stairbuilding from several sectors simultaneously.

[scifista42]

Does the problem also occur in -complevel 9? And in ZDoom? If yes, the problem is most probably with your map, if no, there might be some engine bug. Actually I thought that stairbuilding from multiple sectors should work okay.

[Memfis]

eh nevermind there really were joined sectors
me stupid :(