Quote Originally Posted by strelitzia View Post
The site was using FEC up until the recent upgrade to 1.5.7, so no idea if OPC would have the same issues on an older version of zen cart.
Yes, all bug fixes listed in that thread have been implemented.

To be clear, I have no issue with the form at all when OPC page first loads. But as soon as a shipping method selection is changed, the class is removed from the payment method fields, breaking their layout. I can only assume something in the OPC code is doing this as it doesn't expect that class to exist. They still perform their task, just don't look pretty.
OPC's AJAX handler (which comes into play when the shipping method is changed) loads the current template's version of the various tpl_modules_opc_*.php files.

Are there, perchance, some leftover FEC files that are coming into play?