When waller is placed in its U shape it is optimal for gameplay, creating many situations that are interesting. Sometimes it spawns sort in a Z shape which is good. Just about everything it does outside works great, and can be very fun.
When waller spawns near a solid object, like a wall or statue, it spawns as an unusual shape. Not like when it is placed outside away from solid objects.
When waller is used indoors it naturally creates many situations where escape is impossible , because of almost always being near a solid object. Sometimes it "jails" the player without that bug (which still exists in 1.0.7). Often when it spawns strangely there can be no escape so death is the only option for players wanting to escape the walls.
Therefore, I think blizzard needs to fix waller overall. It needs to spawn better when it is next to solid objects. Indoor it may need to be smaller to prevent too many impossible situations.
TLDR: Waller needs a some redesign especially indoors to make it a challenge for players not an advantage for monsters.