Strange drag/drop behavior from iTunes to Cog

For quite a while I've been enjoying the use of iTunes and Cog together using iTunes for my main output and Cog with an iMic for preview. And I especially like how tracks can be dragged back and forth between iTunes and Cog.

Recently, I downloaded (legally, from emusic) some songs that can't be dragged from iTunes to Cog. When I try, Cog doesn't recognize them, or indicate that anything happened --- they just don't show up in the playlist. The songs don't seem different in any significant way from ones that can be dragged over. When I was trying to figure out what the problem might be, I noticed that the songs can be dragged to Cog from the Finder, they appear in the playlist, and they can be played.

System info:

3-year-old MBP
OS X 10.5.8
Cog 0.08 (r1934)
iTunes 9.2.1