Jan 22 2016
Global/central login seems to be completely broken - I have to log in with every wiki. May be related to the issue posted here.
Happened again today: https://commons.wikimedia.org/wiki/File:KutlugAtaman.JPG
Was overwritten, reverted by me and intermediate file deleted. Despite multiple purges the deleted image is still shown although some thumbs either show the most recent version (or have not been updated from first overwrite).
Dec 6 2015
Another file to run experiments with - Logo was removed but still shows in bottom right on many thumbs.
Nov 30 2015
geographic location may play a role here but then we would have a data sync issue somewhere. The thumb from first file is still wrong (multiple browsers tested, purge had no effect), full screen version may be OK. The second image seems to be resolved.
This is actually a major problem if a purge command is not passed through at all.
See https://commons.wikimedia.org/wiki/File:Jennifer_Winget_at_the_launch_of_Watch_Time%27s_magazine_11.jpg and there may be many more of them
https://commons.wikimedia.org/wiki/File:John_Lennon_Rock%27n_Roll_-_Hamburg.jpg is another one