I filled this originally in the Jalbum thread, but it appears the problem is specific to the Tiger skin, so filing it here.
I just upgraded from JAlbum 12.7.2 to 14.1 and am re-generating my albums to use the Tiger skin. I found an issue if the same image filename exists in multiple directories, even though the image itself is different. In these cases, the folder thumbnail that is used is duplicated on each of the different folders. I assume there must be some caching going on using the filename as the hash key, but this will not work correctly if the same filename exists in multiple directories as is my case.