There appears to be a race condition of sorts. I can reproduce it within a minute or so of clicking around but I've not found a consistent pattern.
- https://commons.wikimedia.org/w/index.php?title=File:AS12-47-6987_(21659597215).jpg&diff=next&oldid=529987348
- Go "next diff" a few times.
- Go "previous diff" a few times.
- Repeat.
Actual result:
For no apparent reason, the wiki is preventing me from navigating elsewhere, on the incorrect assumption that some edit or other input has been entered by me and that I would lose that by navigating away.
To try and attribute the issue to something, I looked at the following state from the console:
//> $('textarea')
Object { length: 0 }//> window.onbeforeunload+''
"function(){var allPanels,
hasChanges;allPanels=Object.keys(statementPanels).map(function(propertyId){return statementPanels[propertyId];}).concat(captionsPanel);hasChanges=allPanels.some(function(panel){return panel&&panel.isEditable()&&panel.hasChanges();});if(hasChanges){return mw.msg('wikibasemediainfo-filepage-cancel-confirm');}}"It seems WikibaseMediaInfo is a likely suspect here.