User blog comment:Kirkburn/Technical Update: September 5, 2016/@comment-5645428-20160907030816

This has existed since the feature was introduced. The Special:ChatBanList list results are never cleared in the instances of bans expiring (as you would expect and as it applies for Special:BlockList). However, they are cleared as long as a ban is manually ended by a chat moderator before the ban has expired normally. This issue causes the ban list to extend seemingly endlessly with countless expired bans, making it incredibly difficult to locate those which are active.