Screensaver - iTunes shows only Book cover art

I have a large iTunes library (700+ GB) with music, TV shows, Movies, podcasts, and books. When I use the iTunes Album Artwork screensaver in the System Preferences panel, I only see the album artwork from the books. I never see any music album artwork. The book artwork includes podcasts and audio books.

How do I get it to show my music artwork instead of my book artwork?

I'm running OS 10.8.4 and iTunes 11.0.5 (5).