Take a look in your Library under Backgrounds to see if there are a bunch of capture graphics listed there. If there are, then you have the captures all right, you're just not seeing them in the slide views. It could be that you have Master Slides assigned to these slides and the Master Slide graphics are sitting on top of the screen captures.
Be sure you have a blank (child) master slide and assign that one to the slides. If the objects you are seeing now sit on the main master slide, you can still create a blank child master slide for which you uncheck the options 'Show Main Master Slide Objects' adn 'Use Master Slide Background' in the Properties panel of that child master slide.
If you want to have the captured slides fitting in the central rectangular space, you'll need another approach: knockout master slide:
That did it! Thank you!
Great to know, this help a lot, thanks!