Reported by BlackcurrantTea at https://en.wikipedia.org/wiki/Wikipedia:Village_pump_(technical)#Page_stuck_in_pending_changes. I was able to reproduce in the enwiki sandbox.
**Steps to replicate the issue** (include links if applicable):
* find a wiki with flagged revs installed. maybe enwiki beta cluster? it's not on testwiki
* pick a namespace flagged revisions can protect pages in
* use admin account to pending changes protect a page with 5 minute expiration
* use logged out user to make an edit, which goes into the pending changes queue
* wait for pending changes protection to expire in 5 minutes
* purge
* null edit
**What happens?**:
* no matter what you do, the formerly pending changes protected page stays in the list at Special:PendingChanges, with no obvious way to remove it
**What should have happened instead?**:
* the formerly pending changes protected page should not show up at Special:PendingChanges at all anymore, since its protection has expired
**Software version** (skip for WMF-hosted wikis like Wikipedia):
**Other information** (browser name/version, screenshots, etc.):