I LOVE your gallery - thank you so much for writing it!
I found and fixed a tiny bug that was cutting off the bottom borders of the tallest pics in the slideshow. Problem was that the height of the ngg-slideshow div was the same as the height of the tallest image, causing the lower border of the image to fall outside the div and get cut off.
I fixed the problem by changing lines 119 - 122 of nggfunctions.php to:
$height = (int) $height; $divheight = $height + 20; $out = '<div id="' . $anchor . '" class="' . $class . '" style="height:' . $divheight . 'px;width:' . $width . 'px;">';
That gives the image a little padding on the bottom, and the border shows up perfectly now.