Been having a problem with MC11 for a while...and the same thing happens in 12.
Basically the "No Images" Task Smartlist doesn't match up with missing thumbnails in my library. I've got numerous albums without images, but only a few of them show up in the Smartlist.
I've tracked it down to the Image File tag (like, duh...i'm slow like that)...the SmartList only checks for whether its blank - not whether the file it points to exists.
Is there any way i can clear the image file tag if the image file doesn't exist? or at least identify those files that point to invalid image files?