Is slideshow causing "scrollto" to skip 1 past selected image?

in this page

can any one offer any suggestions as to why the “<” “>” and clicking aon the image(“advance-link class”) all carry different scroll to behaviors? clicking on “>” scrolls the thumbs one past the selected or main image

clicking on the “<” scrolls so the selected thumb is in view at all times but at the distance of one image away from the top

clicking on the main image scrolls so that the selected thumb is always visible at the very top of the thumbnail div

am i right to be focusing on the gallerific.js

why do these these three navigation options affect the scroll differently? is code for the slideshow causing the scrollto behavior to skip over the image using the “>” arrow?

It looks like there’s a genuine off-by-one error occurring somewhere.