"Love" Designation Keeps Getting Undone

I have set up a playlist of all the songs that I have "Loved" but every time I sync it with my iPhone a few specific songs don't show up on the playlist on the iPhone. They show up in the playlist on my desktop. These are songs that were purchased through iTunes. I have tried deleting and recreating the playlist and the same thing keeps happing. I "reLove" the song on my iPhone and they appear in the playlist BUT anytime I sync my iPhone they go away. Any suggestions?