Hello. I'm just throwing this up here for information, as I think it's a nuanced glitch in the code somewhere, but it's likely an extremely-low priority fix, too.
The problem that I discovered is that if you have an item that has a Moviedb code that exactly matched the TVdb code for another media item, favoriting and un-favoriting either of them also favorites or un-favorites the other.
If you want to replicate the issue, try using The Big Bang Theory for TVdb and Louis C.K. Live at the Beacon Theater for Moviedb. Both have ID code 80379 from their respective metadata sources.
Using those two, I tested all the combinations of which one I favorited first and which I un-favorited first, and the result was the same each time - they both became favorites or were removed from favorites simultaneously.
To remedy the situation, for now at least, you can remove the code from either item in the metadata. For example, I went and edited the Louis C.K. movie metadata and blanked out the Moviedb code from, and then checked the box to not allow changes to the metadata for that item. That solved the issue, and disconnected the two for favoriting purposes.