Complete orders without a customer account

I'm required to fill out the customer field to continue to the payment and completion step.

The expected result is that the order is assigned to the anonymous user if no existing user is selected and no new customer is created.

This issue also reoccurs when adding a customer, continuing to payment, and going back to the order - the customer isn't shown in the field and you're unable to go back to payment without looking up the user again.