TF Labyrinth - Treasure Rooms Pre-explode?

[Targren]

I've cleared three or four labyrinths out and I'm starting to get a bit irked, honestly. Every single time, the "secret vault" treasure rooms are pre-bombed out long before I even reach them (I say "long" because even the blocks that are normally left over from a blast have since despawned) , so I've never even gotten the chance to try to figure out the trick to get in. And I *really* want me a Mazebreaker

Anyone have any idea what's causing this? Is it just horrible worldgen luck?