import fails when updating on duplicate, adding to group, and multiple duplicates exist

When:

• importing contacts
• update on duplicate selected
• indicate that you want the imported records added to a group
• there is two or more dupes in the database already

CiviCRM outputs a fatal error:

DB Error: value count on row

During the import process, all duplicte contact_ids are added as a single, comma separated value in the _newContacts Array.

The code that adds records to the group expects one contact id per value.

I think the correct behavior is to only add the first duplicate contact id to the group.