Contact Import - Update does not work

After initially importing contacts, when attempting a subsequent import that updates those contacts, the Import reports success but does not actually update the contact's info.

This was recreated on http://drupal.demo.civicrm.org

Import > Select Import1.csv
Check "First row contains column headers"
Leave all other options as defaults
Map to the following fields: External Identifier, First Name, Last Name, Email (Home), Street Address (Home), City (Home), State (Home), Postal Code (Home)
Complete Import
Search for imported user reveals that all fields were imported successfully

Set Contact Matching rules to: first_name AND last_name AND email

Import > Select Import2.csv
Check "First row contains column headers"
Select "Update" for duplicate contacts
Leave all other options as defaults
Map to the following fields: External Identifier, First Name, Last Name, Email (Home), Phone (Home)
Complete Import
Import reports success - Search for user reveals that Phone was NOT added to the user's contact info

This test was done with Phone fields. I did not test other fields on update.