The thumbnail shown in Album View panel is the first (00*.jpg in the cases I've uncovered) listed image file even when an appropriately named cover image (folder.jpg, cover.jpg etc) image exists in the directory.
The result is a different image in the Album View Panel to the one that shows as the album cover when you select the album in either album view panel or library panel.
I have the preference set to prefer image files in directory to embedded image in audio file.
The result is a different image in the Album View Panel to the one that shows as the album cover when you select the album in either album view panel or library panel.
I have the preference set to prefer image files in directory to embedded image in audio file.