Here's a strange one...
I'm building the checkout process for the shop, once the user has clicked through to checkout they are presented with a login or register screen. For existing users the perch_shop_addresses_set will not have been set so they are presented with the perch_shop_order_address_form asking them to choose a billing and delivery. However the form shows 'Login' on the submit button rather than the 'OK!' from the template.
The form works fine and the addresses are set, but obviously 'Login' makes no sense to a user who has just logged in.