Why do some local tracks no longer appear in starred list?

[MartinHickford]

Alot of my playlists contain a mixture of spotify tracks and local tracks (usually bonus tracks from albums I have on CD, but aren't on your library). For some reason, apparently at random, some of these local tracks (all mp3s) the Artist and Album info is grayed out, even though it's the same as the info on the Spotify tracks. I'm also unable to add these tracks to 'Your Music' and they don't appear when I add them to my 'Starred' list. The tracks play fine, but it's annoying not being able to add them to my starred tracks.

This problem is apparent on OSX Mavericks, and iOS - all latest versions. I've tried reinstalling on both and removing the tracks from my Library and placing them back. No luck.