Using "set random wallpapers" option includes wallpapers from untoggled folders
In the folder list on the top left, you can toggle/untoggle folders to get them out of the list of selectable wallpapers.
I would expect that the "set random wallpapers" menu option would draw wallpapers among the items in the filtered list. Instead, it draws among all images in all folders, including unselected ones.
This is surprising because one of the folders in my list is my ~/Images folder, which mostly includes screenshots and other non-wallpapers images, and which I leave untoggled most of the time, but can still be drawn when I click the random option.