"One Address should be marked as primary" error, though default address shows as Primary

The "One Address should be marked as primary" is shown for individuals where there is no Primary address record but the UI has generated an empty default address. The Save logic doesn't recognise that the user is being shown this address.

Discovered in Joomla version and reproduced in Drupal demo.

To reproduce:

• create a new individual with first name, last name and email
  [contact has no Primary address record]
• open the individual for editting
  [screen shows an empty address whose location-type is the system default. It is marked as Primary on the screen]
• add a non-primary address
  [system complains "One Address should be marked as primary"]
  [the screen still shows a default address marked as primary]