When user adds a Site, and a thumbnail is added to such a site (either automatically or manually), such a thumbnail is added as an image to user's photo albums (in a "hidden" folder). If user deletes the image from photo album, then image is deleted from the Site's description.
Shouldn't the Sites' module be independent from the other modules in that a site thumbnail should not be treated as part of the user's photo gallery? Thumbnails for sites should be treated as that, thumbnails that can be added, deleted or updated from within the Sites module irrespective of user's image galleries.
*Tested on BoonEx's online demo for latest B8.1