When you are sorting gallery images the insertion line is not displayed correctly. When you move a thumbnail, the insertion line displays in the incorrect spot on top of the thumbnails and not in-between the thumbnails. The sorting will function correctly if you move the insertion line far enough over, but it does not display correctly so you can accurately move a thumbnail in the correct sort order.
See screenshot: http://cl.ly/2k032x0B170h0s0s3413
I have confirmed this problem on 3 separate WP installations and with NextGen Gallery 1.9.1 and 1.9.2