Last modified: 2011-01-25 00:36:54 UTC
When you choose "upload a new version", you can upload an arbitrary file type. For instance, you can upload a gif and then reupload a BMP file on top of it. By default this will succeed, because by default the "ignore warnings" option is checked. This cannot be the intent. The ignore warnings option should probably not be checked by default.
The upload form itself only gives the warning "There's already a file with that name. Do you want to overwrite it?", and it does not say anything about the changed filetype either.
This issue is fixed in trunk, but still broken in wmf-deployment.
Probably fixed with the recent deployment?