I'm still trying to track this one down. On my screen, I have no empty spaces for the apps I've pinned but every few days or so I look and notice a tile has vanished. This time it was oddly enough my "Flyby" app tile, but others have simply vanished from my 920 screen. I can't say if it is the coordinates of the tile because it seems to be from the same generally area affected, or something else. I just installed 3 new apps today so could it be related to that? I have to watch. Not the end of the world but its weird.