Q: What are these black cells?
A: See the description page, which has been updated.
Q: Why did you put them in?
A: Because you wanted me to. See, I would think you prefer that I could give you puzzles to enjoy. For me to give you puzzles, I have to be sane. For me to be sane, I have to not bust my brains out trying to get these @#%$! stairs to work like they should. For me not to not bust my brains out, I have to take some liberties, like black cells. Therefore, I put black cells in because you would prefer that I did so.
I don’t know if you can tell from solving them, but every one of these puzzles has been a nightmare to construct, except for the asymmetric one. I might have to drop the symmetric room restriction entirely.