I have a follow up observation that may be a contributing factor. I've been trying different templates to see if I can find one that will work without modifying the code. In testing with the default Protostar template, I noticed that the login/registration page appeared to be working correctly, until I placed any module in the right column position. The form displays right over any module in that position.
Out of curiousity, I took a look at the login/registration page here on the Hikashop site. There are no modules on the right, so it appears to be working, but if you resize your browser while viewing that page, you can see that the registration fields break out of the template there too. It's only a small overlap outside of the template, but it looks like there is something in the way that page is formatted that behaves differently than any other page in the software.
Do you have any suggestions as to what might cause that particular page to break out of the template, even here on the HikaShop site, when no other pages appear to do so?
Regards,
Mike