UPDATE and did more research. It hasn't really - so this has kind of turned from an "answer request" to a bug report, sorry:
Here's what's going on:
On parcel banlists: regarding the number of people on the banlist:
If you're at 97 people, you cannot go down by one to 96 people, but you can go down by two or more to 95 people or less. --- If you're at 95 people, you cannot go up by one to 96 people, but you can go up by two or more to 97 people or more.
The magic number seems to be "96".