Ok still on /members any unchecked box will trigger a removal notification at the top, for all members in the list. So let's say all I'm doing is revoking membership for user x. The note for user x will say I also removed them as a moderator and as an admin *and* I'll get notes for all other members as well even if I haven't made any changes for them.
Also, while unchecking works, checking doesn't for me. I can't make anybody anything or give them posting/unmoderated access via this page.