billing information absent / incorrect on membership contribution confirmation pages

A major problem occurs with presenting billing information on membership contribution pages, in that it doesn't appear on forms in certain circumstances, and in other circumstances, showing missing information in receipt emails:

To recreate:
1. Create a contribution page with a) membership section enabled, b) separate membership and contribution amounts=true, c) allow additional contribution amounts=true
2. Proceed through live form, and do not enter an additional contribution amount.
3. Observe that on the Confirm, Thank you, and email Receipts, the Billing Information, and Credit Card information is not present

4. Repeat above but enter an additional contribution amount, and see that it works correctly.

5. Modify the contribution page so that separate membership and contribution amounts = false.
6. Test the forms and see that the sections are present, but bad information is being sent, e.g. receipt email with 'Billing name = Array'

Note that information is being correctly sent through the payment processor, but it is the parameters used for form presentation are not being set correctly.