My DVD drive no longer recognises DVDs correctly, and I'm not sure how to correct this.
On startup, Explorer displays the drive as DVD Drive (E:) overlaid with a "DVD" label
(I have 2 hard disk partitions, C: and D:)
However when I insert a blank (writable) DVD-R, the icon is displayed as CD Drive (E:)
Right-clicking on the drive icon results in an slight pause, then Explorer displays the context menu, in which all the entries are indented to the right:

Double-clicking on the DVD icon (which I would expect to launch Windows Media Player) instead causes Explorer to display the drive contents, so I just see a heading "Files currently on this CD", and underneath this is the icon for the VIDEO_TS folder.
If anyone's interested, the drive is an HL-DT-ST DVD+-RW GSA-H31N.
This is not a hardware problem: I can play DVDs in the drive using mplayer:
mplayer dvd://1 -dvd-device e:
...can play the DVD just fine; but Windows can't.
Before anyone asks: No, I don't have a restore point from before this started happening, so I can't just revert the system.
Because of the context menu appearance, I think there's some driver or shell extension disrupting things.
I've had a look at the Filter Drivers, thinking I need to remove something, but I'm not sure what should be there, and what shouldn't.
Can anyone offer any ideas for diagnosing this problem?
Update 2010-08-26
I've removed upper and lower filters, as instructed in this Microsoft Support article, and the Roxio Drag-to-Disc reference has been removed from the context menu along with the left-indentation.
However, note that the context menu does not have the usual Open/Explore/Search entries.
When I double-click on the icon, I get the "Copy CD to CD" behavior, and Explorer shows "Files currently on the CD".