Our registration page simply reloads after submitting the form. The user account is created but the payment selection screen does not appear.
I was able to isolate the issue to a conflict with W3TC (W3 Total Cache). I've attempted to put the registration form in the "Never cache the following pages" section of the Page Caching for W3TC but that has not helped resolve the issue.
You can replicate this issue by vising http://www.cagle.com/heroes (click on one of the subscription rates on the right hand side).
I've granted access to our backend as well.