Games show up as in library when on their page, but not when i'm actually in my library
Free to play games that you haven't spent money on will disappear from your library after they're uninstalled, but Steam will keep track of the time you've played them and mark them as "In library" on their store page.
If you have spent money on a free to play game, on the other hand, when uninstalled it will still show up in your library as a darker shade of grey, like games you've purchased.