When I delete a picture from the hub (using the Mochi interface and remote), the thumbnail file for it is not deleted. This is also true if a picture folder is deleted - the thumbnail for the folder is also left behind.
These thumbnail files are located in a hidden folder structure at the root of the network share called .wd_tv\thumb. The thumbnail files are named the same as the photograph but with a .thumb extension tacked on. ‘Picture.jpg.thumb’ for example.
If I then replace the deleted picture with a different picture but with the same name, then the hub displays the new picture but the thumbnail of the old picture.
This is buggy.
If I delete the thumbnail file via the network share, and then browse the hub and view the photo again, the old thumbnail has been restored. It is getting cached somewhere.
The only way I found to permanently delete the old thumbnail is to delete it via the network share, then immediately do a hard power down of the hub. When it is powered up again, and after it recompiles the media library, the thumbnail has been replaced with the correct one.
I can see that this little problem could get rather annoying after a time and many photos were added/deleted/moved/renamed.