When playing entire 'Genre,' does 'Playlist' reset?

My most common method for playing music on my Squeezebox (through Logitech Media Server) is to select a Genre and let it play on random. My favorite genre has 842 songs. When I begin playing, there is a message: 'Playlist full. 500 of 842 tracks selected.' So apparently, there are only 500 songs that are eligible to play. As often as I play this genre, I'm starting to notice, there are some songs that play often and some that never do. What I'm wondering is, are 500 new songs selected each time I play that genre, or is there some memory, and it is always the same 500 songs that have been selected in the past?

Thanks!