I thought that one-way shutters would stay shut if you put them in a dungeon room and entered that room, but for some reason, the door will act like a normal shutter! Why?
1-Way Shutters not working?
Set the Dmap as a dungeon.
I already said that it was a dungeon DMap.
Sometimes the 1-way shutter will open if it's an exit to the overworld. If it is, you have to change it (that happened to me, anyway).
Well, for me, a 1-way shutter opened to the entrance room of the dungeon. All that's in the room currently is a hidden staircase. I'm gonna make a secret exit to the room, but the shutter opens on its own. There are no enemies in the room, and no blocks.
Do you have the Dmap set to a level higher than 0? That's gotta be it.