Default values on custom fields aren't respected when creating contacts via a profile

More specifically: Default values on custom fields aren't respected when creating contacts via a profile WHEN THE FIELD IS NOT IN THE PROFILE.

Found this problem on a 4.3.5 site, just replicated on the trunk running at sandbox.drupal.civicrm.org.

Steps to replicate:

• Create a new custom field group. Create fields in those groups with a non-null default value.
• Create a contact using Contacts -> New Individual, entering only a first and last name. After saving the contact, you can see the default values for the custom fields was entered.
• Go to the Profiles screen, select "Use Profile - Create Mode" for a profile that doesn't include those custom fields (e.g. "Name and Address"), and use the profile to create a contact.
• The custom fields have no default value entered.

FWIW:

• This problem also happens if the profile is included on a contribution page.
• This is a distinct issue from CRM-12748, which happens when the field IS present in the profile.
• The custom group field I tested with held fields for all Contacts.