Any tips on how to diagnose the following problem?

1. I insert a DVD-R
2. I open the disc through nautilus (i.e. burn:///)
3. Copy some files over, press 'write'
4. Nautilus tells me only DVD+R and DL are supported

Not so! I was burning on these DVD-R's until recently with no problem. If something's broken, it's due to a recent upgrade, or else some weird bug in Nautilus that I'm encountering for the first time. Any tips on how I could diagnose this problem?