Maybe, I've experienced the inconsistency and I think it may be iOS interference to make images web compatible. There's an option in the media upload dialog for Compatibility and options are Automatic, some option to disable, and something like Most Compatible.

I do know by the Damus source the uploader sets the content type in the POST request to "image/jpg" if the media is an image, regardless of what kind of image it is.

However, in testing a potential fix I've experienced mixed results where sometimes it uploads with the gif extension and content type but sometimes it doesn't so maybe there's more to it.