Invalid form controls on Billing inputs in Chrome

[RuthAdele]

When using Chrome, and having selected billing same as shipping address - submitting the form causes Chrome to try to validate the HTML5 inputs, but because they are hidden by display: none, they are not focusable, so the follow errors are logged in the console.
"An invalid form control with name='BillingFirstName' is not focusable." (plus all the other required Billing fields)
This means that the form does not submit, and no message is shown to the user. Unless you were a developer, you would have no idea why you can't proceed to payment.

[RuthAdele]

On closer inspection it seems the problem lies with the "same as shipping address" being preselected. So none of the address values are actually copied into the billing fields as per the js function _copyAddress (unless the user unchecks, and then checks the box again).
If we unselect the "same as shipping address" box by default, everything works as expected.