When I tried to upload the first revision of https://commons.wikimedia.org/wiki/File:Terence_Winter.jpg with UploadWizard, I got the error it's a duplicate of that file (well doh) and another file with an unknown filename.

So I cropped https://commons.wikimedia.org/wiki/File:Terence_Winter.jpg a bit, now that's no longer a duplicate. Now UploadWizard just gives this error: Unknown warning: "duplicateversions". I can't upload it.

When using Special:Upload instead, the file is uploaded without any error.

Update: note that now UploadWizard will say "A file identical to this file (File:Test winter.jpg) has previously been deleted.", this was my Special:Upload test. Click "Upload anyway" and you will see Unknown warning: "duplicateversions". This error is not caused by Test winter.jpg.

Suggested solution: UploadWizard should report the file already exists as an old revision of $filename, or (if deleted) produce the same warning as that for deleted files. ("A file identical to this file (File:El pikashu ma chido.png) has previously been deleted. You should check that file's deletion history. If you disagree with the reason for deletion, please make an undeletion request instead of re-uploading.")

Special:Upload could also warn the user.