Thanks for taking your time to read this. Image may be NSFW.
Clik here to view. I didn't want to have to reply to EVERY SINGLE PERSON on these forums that have had this problem, so I decided to just put it as a discussion. Feel free to comment.
It has been proven here (just scroll down, you'll find it Image may be NSFW.
Clik here to view.) what has deleted many player's save files on Mario Kart 8. Apparently, letting the console auto power down on the title screen, very rarely will corrupt the player's save file, causing the game to erase all save data and restore the game back to factory settings. When it does this, for some players it doesn't erase videos on MKTV for unknown reasons.
Hopefully Nintendo will become aware of this issue and patch it, but it appears they are unaware of it at the moment.