I started a thread for this thinking it was affecting my whole iPhoto library, when I export a cropped image I get the original. I thought I'd solved it by rebuilding my library, then realized the issue was only manifesting with iPad screen shots. I tested it on iPhone screen shots too, same issue. Photos taken with any camera, even the iPad camera are fine, I can crop and export those. Any iOS screen shot refuses to export a cropped version. I tried all the different choices for "kind" in "export."
Is this a new feature? You have to be sure to crop a screen shot on the iPad or iPhone before you sync to iPhoto?
Mac mini 2011, Mavericks 10.9.2, iPhoto 9.5.1, iPad Air iOS 7.0.6, iPhone 5S iOS 7.0.6