Stitch Assist Help.

Tried to do a stitch assist with my SX40 today but couldn't get it to work. I shot the first pic and then matched up the second shot to overlap a portion of the first. That seemed fine. But then I tried to do a third shot and it only showed a image of the first shot, not the second. Hard to explain but I've looked at the manual and am not sure what I'm doing wrong.

Any ideas?