ToME: the Tales of Maj'Eyal

In high peak I got a hidden vault stairway, and the vault was one with a bunch of 2x2 rooms you have to dig between, with only certain tiles being diggable. I then found though that I could only access half the vault, and there were more rooms there were no diggable walls to. I then found despite being a no teleport area, I could enter the other half using slime roots. In the opposite corner to the entrance there was another sliding rock that prompts you if you want to open, but on the other side there was only impassable wall.

Just found another vault layout with the same issue, this time there is a long 2 tile wide corridor that makes a u turn followed by a diggable wall into a tiny loot room, which twists around another identical path.