First of all, great job on the new version, Kornel. I did a couple of runs in 0.9.8.7/Win+Sound and I'm really enjoying the new features. I started a new player.dat - seems like a wise decision now ;) - and so played my first new games on easy. I made it to the Phobos Arena, but for lack of a nuke I got killed by Cybie. Tough luck. But guess what...
In the graveyard section of the mortem file I was able to see 'the' staircase. I would never have discovered it in the game without nuking the place. This of course happens because your surroundings are completely revealed when shown in the mortem. You'll probably want to cover up the staircase in the graveyard section.