You can fix the bug in L11:1E by placing the roaches/roach queens in a different order, namely:
There are some other bugs that needs fixing. Here's some comments and bugs that I've found (I put it in secret tags because it contains spoilers):
×Level 1:
3N: It's impossible to return from the south (this is especially unpleasant if you haven't completed all the rooms yet).
3N1E: There are at least five different ways of completing this room. You can either hit the first orb and seek shelter in the alcove to the south OR you can hit the orb that opens the S door and kill the roaches OR you can open the door to the mimic chamber, enter the mimic chamber and use a mimic to hit an orb that releases the roaches OR you can open the mimic chamber and use mimics as protection after you've released the roaches OR you can dispatch and kill the roaches in smaller groups by hitting the first two orbs to the left.
Level 2:
1S2E: I don't understand the scroll. It doesn't matter which direction your sword is facing when you enter the room because you have plenty of time to change it.
1W: The green door in this room is a bit redundant as you can go past it with a diagonal move.
Level 3:
3E: There are at least four different ways of completing this room. You can either open the big door and retreat to the entrance OR you can hit the N, S, E and W orbs and kill the roaches in the narrow passage OR you can use a mimic to kill all the roaches before hitting any orb OR you can open the big door and use the mimics for protection (one mimic is sufficient).
Level 4:
The Entrance: You can go down the stairs on both sides, but I believe that's intentional.
Level 5:
4S1E: E
www...
Level 6:
4N: You get stuck if you exit this room to the north or south before you've completed 3N and 5N. A mimic in the right place (for example above the green door) should do the trick. It would also be a good idea to put a green door on the south exit (so that you don't get stuck if you exit that way before completing the room and 3N).
Level 7:
2W: This room needs a checkpoint at the end of the long corridor.
2E: The invisibility potion makes this room trivial, but that seems to be intentional. You can do this room without it, though.
Level 8:
2S2W: This room would benefit from a checkpoint in the center of the serpent loop.
Level 9:
2W: A checkpoint somewhere would be nice. Great room otherwise.
1W: A checkpoint near the north entrance would be nice; you don't want to wait for the serpent several times.
4N1E: This was a fun room. I was almost going to complain about it being impossible before I finally got it.
Level 10:
3S: The orbs in the serpent loops are not required. I can't seem to find any use for them.
Level 12:
1N: This room is impossible (tar does not spread on arrows)
Secret Level 1:
2N3E: You can either open all the small doors and the red doors and kill the monsters in the small corridor OR you can open the door to the mimics and use them for protection after opening the big door OR you can open the rightmost door to the south and kill all monsters with a mimic.
6N2E: The scroll makes the room much easier, because the brain can't direct monsters through it unless you've stepped on it first...
Secret Level 2:
1S1W: This room needs a checkpoint somewhere near the entrance to the central area. It's quite annoying to wait for the tar to grow for about 800 moves every time you make a typo. Edit: You cannot return from the north (uncuttable tar-blob).
1W: You cannot return from the lower east exit. This makes it impossible to finish the level.
I haven't played all of Level 11 and Secret Level 2 yet (or any level after L11), so there may be other bugs.
