UploadFromStash is broken in MediaWiki 1.18.1.
So when you try uploading a file and it fails with a warning (for example ...this file is a duplicate of...), clicking both "Submit modified file description" and "Ignore warning and save file anyway" buttons don't work - you just get an empty upload form after it.
This bug can be fixed by taking includes/upload/UploadFromStash.php and includes/upload/UploadStash.php from trunk r105822.
Marking this bug major as MediaWiki 1.18.1 is listed as stable. The fix probably needs queueing for 1.18.2.
Version: 1.18.x
Severity: major