Membership creating HTTPS calls when inapplicable

Just like the title says, I am getting HTTPS:// calls at inappropriate times, and all the browsers spit out warnings for insecure content. The easiest way to reproduce is to go the /register/ page, create an account and view the fields for credit card entry (all of which parse ok). If I don't do the checkout, and go straight to any other page, the call is still HTTPS://.

No matter what link is clicked after the warnings, a 'S' call is always made, essentially breaking the experience of the site.

Any ideas?