Thank you for taking the time to play my game and leave such a comprehensive description of the bug you encountered. I will look into this glitch and post a fix.
I ran into the same thing, it might have something to do with going back through the vent and triggering the "I hear something ahead" prompt a second time. Actually, it seems to happen when you return to the screen you first gain control inside, even if it's from the other side of the door.
