Hello,
I replaced the lightbox with fancybox for exactly that reason.
1) download/install fancybox
2) keep the “lightbox” option checked in your theme appearance
3) see here for how it is done:
http://www.onedesigns.com/support/topic/fancybox-and-infinite-scroll-issues
and it all works here:
http://www.photonopticum.com
Good luck!!
M.