iPhone 3GS lyrics not showing up?

I have lyrics for all 1800 of my songs, and i noticed something weird when I play songs on my iPhone. The first song always show its lyrics, but when I hit next/ skip song, it wont show the lyrics. I have to double tap the screen to hide and show lyrics before the words show. This happens to a random amount of all my songs; some show lyrics on the first time, others don't. Anyone know why this happens or how to fix it?