I'm not entirely sure if it's a regression. Marking as such for now.
https://commons.wikimedia.org/wiki/File:Station-Leeuwarden-WLM.jpg has had a new upload, but the 800px thumbnail cache is not being invalided/purged/cleared.
A recent reupload took place removing the watermark, but the 800px thumbnail still has it. Any other random size that I come up with that wasn't cached before does show the correct latest version.
action=purge or null-edit on the description page didn't fix it. Neither did clearing complete browser cache.
Even if action=purge did work, imho cache should automatically be marked invalid/cleared/whatever when a file has been (re)uploaded, just like is done for wikitext cache when an article is edited.