Sorry if this isn't the right place to post, didn't see any other bug threads for this. I entered a mysterious portal on level 1 just after getting the DLC, and have had to save-scum after death a lot in it, if that affects anything. What I've noticed: The portal dimension is infinite? Every portal exit takes me to a new, randomized portal level. If this is intended behaviour (which actually would be really cool, like a New Game+ or separate Challenge Mode, 'See how far you get'), it would be nice to get a warning beforehand. Sometimes upon reloading in the portal dimension either everything, or everything except for creature sprites and liquids is black. I can still see the tooltip from the cursor to tell if I'm hovering over a door, for example, and the map still works. The only way I've found to fix this is to take the portal exit to the next level (using the map to guide me). If the infinite portals is a bug, my vote is to leave it in the game in some capacity, because fighting on like this, quicker paced, without shops or vending machines, and random monster strength is fun. Possibly an optional side-mode?
I don't think it's supposed to have more than 1 portal floor at a time, so I'll file it as bug, thanks. The other thing is a known bug.
I can confirm it's one level at a time, as I blasted my way through the supermonsters with My Chemical Explosion and was taken back to the 3rd floor with the exit. No save/load action happened, so maybe that has a hand in it.