Thumbnail images generated by namespace extension not receiving adornments (e.g., drop shadow)

I've written a namespace extension to represent a remote file system. IExtractImage is implemented to provide an image for the various thumbnail views supported by the Shell. This all works properly. However, I notice that the thumbnail images I generate, when displayed in the shell view, do not have any thumbnail adornme开发者_JAVA技巧nts on them.

According to the MSDN documentation for thumbnail handlers:

Adornments such as drop shadows are applied to thumbnails based on the user's currently selected theme. Adornments are provided by Windows; do not create them yourself. Windows could change the look of particular adornments at any time, so if you provided you own you would risk falling out of synch with the system. Your thumbnails could wind up looking dated or out of place.

So it would appear that the Shell should be adorning the image returned by my namespace extension with the appropriate eye candy (normally, a drop shadow). However, no matter what I try, the images displayed in the shell view are exactly the image I'm returning from my interface. For the sake of covering all bases, I even tried accessing a local shell item's IThumbnailProvider and retrieving its thumbnail image. The returned image was not adorned either.

Is there some other interface I might need to implement in order for this to work properly? What am I missing?

Thanks.