IFrame not working properly on identical sites

Hello.
This is driving me batty, completely stumped. I hope this is the appropriate place for this question.

I set up shadowbox on our development site, and it worked great!
I did the exact same setup on the production site (same server), and the IFrame content won't fill the width of the shadowbox on the production site.

We have a few modules in use on the production site that aren't used on the dev site (CiviCRM, ShURLy, Mollem, Google Analytics) - I tried disabling these but it made no diffference.

I thought it might be the content itself, but both sites are using the same link content being displayed is the same for both sites.

Other than the modules listed above, the only difference between these sites is that the production site uses secure pages

dev site: http://devupdate.itk.ca/test/flip-book-test
Production Site https://www.itk.ca/test/flip-book-test
(see the "read online" links)

The direct link to the content being displayed is https://www.itk.ca/itk_docs/flipbook/EnvironmentalHealthGuides/Environme...

we are using

any ideas as to what is going on?

Thank you