If you click on the thumbnail, the image blows up into a lightbox view. There's an enlarge icon (like an X, with arrows on each corner) in the top right-hand corner of the blown-up image in lightbox view. This enlarges it even further, which is great! You can scroll around and view the super-blown-up image; the expanded view.
BUT... In this view, for some reason, it's impossible to scroll left. You can scroll up, down, and right to see a very zoomed-in version of the image, but you are missing part of it because you can't scroll left. What's that about, and how do I fix it for my client?
The site is not live yet, but I can provide login details to somebody privately to illustrate this issue.
Looks like somebody had asked this question previously but I can't see that it was answered: http://wordpress.org/support/topic/prettyphoto-expanded-image-being-cut-off