Can't burn m4p songs to audio cd

Question

I used to be able to burn m4p songs to an audio CD in iTunes.
This does not seem to work anymore.
If I create a playlist with my m4p songs then burn it to an Audio CD, nothing happens.  If I add a few mp3 files to the playlist and burn it, only the mp3 files get placed in the audio CD.
I'd like to burn my songs to CD and be able to play it in my car's CD player.
When did this feature go away? And is there a way to do this now?

Answer 1

As an update to my previous post, I took one of the playlists with both songs with a purchase date and songs without.  All of the songs were .m4p files.  iTunes only burned the songs with a purchase date.  Some of these songs were from 2003, some were from 2006.  I then deleted 3 of the songs without a purchase date, re-downloaded them, and put the re-downloaded songs back in the playlist.  They now had the current date as the purchase date.  iTunes burned those along with the others with a purchase date, but still skipped the ones without a purchase date.  I have purchase dates dating back to June, 2003, but as I sorted them, I found over 1600 protected files without purchase dates (out of 2700).  I know they burned before because I have some playlists that contained some of these songs that were burned previously.  I also know from some printouts I made several years ago that many of these songs had purchase dates.  It's as though the database corrupted and the purchase dates went missing; now they won't burn without them.  I did open a ticket regarding the missing purchase dates.  We'll see what happens.  I realize that I could delete and re-download most of the songs (some are no longer available in the store), but I'd have to annotate my playlists first, then delete, re-download, then re-populate the playlists.  WAY too much work.