Steps to reproduce:
- upload a file to Commons
- add file to a page in a different wiki and open it in MediaViewer
- upload a new version on Commons
- refresh the page, open the image in MediaViewer again
You will see the old image in MediaViewer.
(reported by Dan Garry)
Caching is important but this could be really problematic in some situations (e.g. image vandalism). At the very least we should track it.