Great game!

1. Level 6, one of the northwest most doors leading to the long west hall appears as a normal door once opened and viewed from a corner tile, then becomes hidden door when facing straight adjacent.
2. Level 4, when approaching the general area of the stairs from the north , the stairs stick out graphically. Once I find the stairs during that visit to Level 4, then come back to the tile north of it, the bug is gone.