ToME: the Tales of Maj'Eyal

I'm on Rak'Shor 2, coming back down after killing the boss. There's a big vault that covers much of the level. I open it up and clear it, but after I'm done there's still a large unopened area. I searched all the walls around it for a diggable square - nothing. I tried teleporting into it from elsewhere in the vault - nothing. Am I missing something dumb?

This has been up for a while with no replies, so I guess either it's not such a dumb question, or it's a really dumb question. Assuming the former for the sake of argument, maybe it's a bug? Is anyone interested in looking at my save file?

All I can think of is that the entrance is blocked by the edge of the other vault.

Yes, I suspected that as well. Thanks, I'll post in the bugs forum.