Having the same problem as Cody, when I click on a black tab to change size, mat, etc, the whole box goes away. It's only a problem in widget/iframe mode. Just to be sure:
At Cody's store, pick the first photo. In the options box, select the second tab, marked 'Mat'. On my iPad and iPhone, the box, tabs and all disappears.
I haven't used the widget on my website because of this. I wonder what might be different about our gear? Mine's an iPad 2 with the newest OS release, using mobile Safari.
Thanks,
Dave