if you quicksave the same frame you die, you will be invulnerable to everything except instant death triggers. the only reason I think it's a health underflow is if you get health you die again. this means you could actually just play the highest diff notorious for being the worst thing ever. I gave up halfway through though this game is incredibly boring

I don't know how I missed this message a year ago but I think I basically found this bug you speak of for my run, but only back when I hadn't realized that I needed vsync enabled for the 2nd to last level, so I was insta-dying each time to the rapidly rising water.

I never did bother figuring it out for the wider run as I didn't think it as being important, but now that I'm thinking about it again upon reading this, maybe if I do come back to this game again I might try figuring that out for the tougher sections like the art museum.