Mailman 2.1.15 doesn't allow admin changes on private lists

I run three Mailman lists on my web server, one browsable and two non-browsable. I wanted to eliminate the footer that gets added to the bottom of messages distributed by one of the private (non-browsable) lists.

When I tried to do this, I would browse to the admin non-digest page, delete the contents of the Footer field, and hit "Submit my changes". This would send me to a login for admin privileges of the list in question. I would log back in, only to find myself on the page I had just modified, but the modification I made did not take place.

I experimented with this a bit, and found that I could eliminate the footer on my public (browsable) list on the same server. So I tried converting my other private (non-browsable) list to be browsable, at which point I could eliminate the footer, and then switch the list back to being non-browsable.

But once I tried to implement the workaround on the non-browsable list I wanted to change, I got the same defective behavior when trying to switch the list to be browsable -- I would get redirected to the admin login page for the list in question, log in successfully, only to come back and find myself on the same privacy page, with no changes having been made.

I saw a report of this behavior on the mailman-users mailing list from the year 2000. It is still going on now in 2023. One would think that some information on how to workaround this bug would have been found between now and back then.

Note that, when I am able to successfully change a setting, I am never sent back to the list admin login page.