MarkoH01: You asked the right question: where is Black Mirror 3. The answer seems to be the solution to the "problem" which is more like a missing feature. "Black Mirror 3" along with "Memoria" are both hidden games. So basically everything works correct - however it would be nice if the hidden games could be omitted from the index list somehow.
HypersomniacLive: You could do it the way I do, and avoid any such issues - place all hidden games at the very end of your library. This way any moving around of games stays within the range of the visible ones.
But in case it's doable, and adaliabooks implements it, I'd like it to be optional, as always. :-)
It should be possible somehow... I'll have to have a poke at it and see what works.
In the meantime, if the hidden games in your list annoy you you should be able to remove them manually by exporting the list, removing the game and re importing it (though do keep a back up of the original export in case something goes wrong). It might get re-added but as far as I remember of how everything works it shouldn't.