I had a similar problem, and it was fixed by doing the power-cycle of the WD SMP (hard power off and reboot). I did not need to delete the .wdtv folder or do a manual rebuild the media library. Merely rebuilding the media library without a reboot does NOT refresh the thumbnails.
However my experience has revealed another SMP coding oddity. I had a folder with 15 video folders in it. As a test, I created a thumbnail for the first file. It worked straight away (no reboot), and it was used as the thumbnail for both the first video file, and the folder overall.
What’s odd is that when I added all the other thumbnails, they did not show up until I did the reboot. So WD SMP is coded to think that once the FIRST thumbnail appears in a folder, it won’t automatically scan for thumbnails in that folder ever again, even if thumbnails were missing for some of the files. If you add more thumbnails later, or even overwrite previous thumbnails with new ones, it doesn’t rescan the folder, it just ignores them.
So the lesson is - add all thumbnails to a folder in ONE GO, before you browse that folder on SMP. Don’t add them one at a time unless you want to reboot the device every time you add new thumbnails to that folder.
