So I have a story to share about this game which happened to me about 5 years ago, playing this on the NES.
I was in the process of doing a full playthrough, mapping out the entire game on pencil and graph paper. Real old-school stuff. Anyhow, as I was going through and mapping out Level 9, I made my way up to the top-middle part of the map and PASSWALL'd through into the room containing the tile giving you 1,000 XP (circled on the pic).
I have no idea how or why this next part happened, but immediately after I cast PASSWALL, the game went directly to the ending! At first I thought the game crashed due to the seizure-like graphics, but it was the legit ending scene with the 'Hall of Fame' screen and all that. I ended up resetting and continuing, and didn't have that happen again on the 8th floor. It did happen to me one other time later on in the game, though.
No idea what causes this to happen. Just wanted to throw this out there to inform that there's something glitchy within the game's RNG which can cause a game-end glitch.