I see it now - both the buggy level and the level above it (if accessed from the bottom entrance, i.e. from buggy level) have the ability to exit the right side of map into either a non-existent level ("harmless" game freeze) or into another level in a location without any solid ground, which leads to falling out of bounds into non-existent level even after page reload (because player location is saved from previous map change).
I stayed up too late working on that buggy level, obviously. I fixed up those levels to protect future players.