This is after the release of the June 22 update; I'm not sure if it is linked. After beating Underhalls and going to the exit, there is a room opposite the exit from the building that sometimes has a chest. In this scenario, the path to this other room is completely blocked off, which you can see there is a wall, and a space on the map that shows these two rooms are separated. Could this be a bug in Dungeon generation?

Versions did not list the build: 1.2.1.0_4274376