Well damn... Guess I got unlucky in my run today. I didn't know that you need the blue key. I tried to open the staff only room with the pizza with the black key, and now I don't have it anymore, because of this belt bug. Do I need something else to get the blue key?
The blue key is located in this room with the pink circle and the blue key icon, right next to Viktor's room (the room with the triangular animal crossing sign.) The rooms enclosed in a violet circle are the rooms that can only be opened with that blue key: pizza room, server room containing the red key with possibly math notebook (completely useless red key serves no purpose), and the bunker/start of level shortcut. Oh, and what do you you mean by belt bug? It works just fine for me, just hold TAB and press ALT, it's no longer MMB to store artifacts.
