On the "Upload warning" page, the "Return to the upload form and choose a different name" button sends the user to an empty page (just the title "Upload file" is shown). That button is named "wpReUpload". I remember there was some confusion about "reupload" URL parameter naming collisions when the re-upload stuff was introduced (see bug 17193, comments 3 to 5). Maybe this is related?
Version: unspecified
Severity: normal