Banned Posters become Un-Ignored

I have put some posters on my ignore list who were later banned.
Their names are no longer on my ignore list and their posts are now showing up in threads where they participated. Unfortunately, I don’t seem to be able to re-ignore them. Is there any way to ignore someone who was banned and to continue to hide their posts?

I just tried putting a banned person on my ignore list, and it seemed to work. I think there are a couple of different ways to ignore a person. I did it by going to that person’s profile and clicking on a link in the upper right corner that says “Normal” (or “Muted”, or" Ignore"). I changed it from Normal to Ignore. I then went to my own profile, looked under Preferences/Users and saw that it took.

Could this issue be related to the following?