Go to http://commons.wikimedia.org/wiki/Special:Upload
Choose a file, set as name "[[É]].jpg" and press Upload.
You get a warning that the name has been changed to «--É--.jpg», please modify the description and try again, and three buttons:
- Send modified description (the description wasn't at fault, it was the filename, which wasn't modified in the input)
- Ignore warning and upload anyway (this is not ignorable!)
All of those buttons send you back to the original Special:Upload (although with the fields prefilled) instead of finishing the upload from the stash.
Same error if the warning instead of coming from the filename was due to uploading a duplicate.
Version: 1.18.x
Severity: normal