Occasional problems with slideshow "navigation bar"

Hi,
My site is tanveer.smugmug.com
I have seen a weird problems with the slideshows, and it happens always(windows XP with Firefox 3.6.8).
I have not experimented with other browsers though.

Here is what happens.
When doing slideshow, I can move the mouse, and it shows me the top bar which has small thumbnails.
There are arrows on extreme left and right top, so the nav bar selection can be moved.
Sometimes, nav bar goes blank, and then when it comes back, it shows the first set. I may be on the 100th image currently, but the nav bar will start showing first 20 or whatever.
I have to repeatedly click the nav bar arraows to get back the point I was in the slideshow full screen page.