Problem with creating Users/groups for a multi-select User/Group Custom Field in a CSV import

A CSV import is allowed to include multiple user values for a multi-select custom field.
eg A line of the file could look like:
Bug,Some stuff is broken,"John Belushi,Penelope Cruz"

If you have auto create Users turned on, then a single user is created whose name is "John Belushi,Penelope Cruz"
when it should be creating 2 separate users.