The thumbnails are sorted in the slide show based on their geometrical location. Left to right, top to bottom. But if you want, I can provide a tweak that disables the sorting. In this case, the images would be displayed in the stacking order of their thumbnails. So that you would have a full control over the order of the slide show.
EDIT
Here it is. Drop it on your page and it will not be sorted.
Bookmarks