Problem... no walls

[WindexGlow]

Seems like the devs forgot to add a portal somewhere.

To optimize games, there are rooms and portals.
Rooms contain parts of the level; for example a hallway.
Portals connect a room together.

When you are not in a room, that room is not being rendered unless a 'Portal' is in your line of sight, and connected to that room.

So unless this happens 24/7 it's just a small bug.