Changing the video file causes thumbnail to update

[mrname]

If you have an existing video object with a thumbnail, changing the video file will also cause the image thumbnail to be recreated. This makes perfect sense if the thumbnail is auto-generated (otherwise it would not match the new video file). However, in a situation where a custom thumbnail is used, this means that you would need to explicitly re-upload the custom thumbnail every time you change the video file. The desired result is that you should be able to change the video file without wiping out your custom thumbnail.