We use Invision prototypes extensively to conduct usability tests on our features. One major issue that I have noticed is that the user is allowed to go backwards and forwards in the series of images.
There should be an option to not allow that as that defeats the whole purpose of conducting a usability test. We stitch the screens according to the task flow and allowing the user to skip that and move ahead leads to more confusion because they can't figure out where to go back.
I'd suggest you have a usability test mode that can enable designers to control such things.