I...uhm...nodrawed every surface on my map that the player can't see, as you all have adviced, and somehow that made one of my buttons go berserk. It seems like the trigger is triggering like 10 times a second without anything touching it, making the door and button vibrate insanely and the indicator strips flash epileptically. And as far as I can see, there's no difference between it and the other buttons.

Any ideas? or do I have to remake it?

Yeah that happened to me as well, although i don't know what causes it, right now im trying to figure it out, messing with the settings of the button it self and such, perhaps its just something stupid, as that always happens within Level Design. I'll tell you a fix if I find one!

EDIT: I'm using the cordon tool, and it appears to have stopped, but thats just with that, i think maybe something somewhere in my map is causing it, though i don't know what. The strangest thing is that it happens only when the player opens two portals.

By the way, did you follow the tutorial on the VDC?

Haven't used much of the VDC tutorial, as my map still consists of only two quite small rooms, so there's not that much point in splitting up anything arealportal-style or something. As for much of the other stuff there, I don't understand all of it, so no I haven't done much of anything on the tutorial yet.