The staircase on D48 does not switch to 'up' after nihilist ending
Ascending after the nihilist ending, the staircase on D48 still only goes down, leading to an ignominous YASD. (Feel my pain...)
If this is intentional (as in, player should pull the levers after coming back through the gate), there should probably be a cue for the player, since at that point the game is doing its utmost to make the player HURRY and get out of there. I'm inclined to think this is a bug though, since the staircase on D50 lets you leave, but the one on D48 won't so the player has no warning whatsoever that the way up is blocked.