I have never seen this before. Take a look at the picture below. It's on level 1 with a new character. I had two levers and when they opened the walls, this is what I got. By the way, I was trying out the Clockwork Knight v2.5 mod for the first time. This is probably an extremely rare occurance. Well off to more killing.
I had one, on a vanilla build where the level opened a small hatchway that went around a door that I could have opened naturally lol. I should have taken a screenshot