OH MY, ok, you need to close ALL THE DOORS leading to the room you want the effect to stop, not only the adjacent one! I was closing the door at the left of the "tentacle room", thinking that would be enough, but the effect was going all the way down/left/up so I had to also lock that one ^^. That makes sense now that I nkow about it, but a little visual effect coming from the doors would probably have helped me understand ^^.
Now my understanding of your concept is waaaaaay better, and your game makes a lot more sense (and fits in the theme more than what I thought)! I'll try to reach the end and adjust my ratings accordingly, thank you for your help ;)