[Plugin: Portfolio Slideshow Pro] Duplicate images in lightbox

I recently upgraded to WordPress 3.5.1 from 3.4, and now Portfolio Slideshow Pro isn’t working as it used to. When I click an image to view the slideshow in a lightbox, every image appears twice – so instead of having four images in the slideshow, I have eight. The thumbnails still work properly – it’s only in the lightbox that the problem occurs. Any ideas?