This is with the "AD Group to Profile: Advanced Settings" > "When to update" set to "When creating and updating a user" and the default profile ("If value is null apply default value") set to "Identity User".
I created a user in AD - icUser01 - and added it to 2 AD groups - ProfileGroup1 & ProfileGroup2. After I started up IC, I mapped ProfileGroup1 to "Chatter Moderator User" and ProfileGroup2 to the lower priority "Inside Sales". After a full recon, icUser01 was created in Salesforce and assigned to the higher priority "Chatter Moderator User" profile, as expected. (This is part of the check_profile_mapping_with_update_when_creating_and_updating test.)
I then updated icUser01 by removing it from all AD groups (other than users). After a full recon, I expected the updated icUser01 to get reassigned to the default Salesforce "Identity User" profile, but it wasn't. It was still assigned to "Chatter Moderator User".