In room 15710 of Knight Mansion (any difficulty), it is possible to jump up into the area where all the scorpions wait after pulling the switch that releases them. If you do, you can't get out; Jack is stuck.

This next applies only to Knight Mansion Hard, I think. If, after you obtain the first blue key, you go immediately to the top right and open the blue door that guards a shield and some treasure, you won't be able to get through the blue door that leads to all the other blue keys in the mansion. Stuck!

I think there was another that I was going to report, but I forgot it. :( But, on the plus side, I made spot #9 on the global list, which I didn't think would happen to me on any mansion, let along a hard one. :)

That thing's only found in Normal and Hard.