[otrs] Can't find user on "Customer User <-> Groups"

Hello, We are using OTRS version 2.3.4  Our (internal) users login at customer.pl and are able to authenicate against Active Directory.  The problem is that there are several new users that were added to the Active Directory after the initial sync to OTRS.  These users can login successfully and I can find them if I search in Customer Users.  But for some reason, I don't see the newly added users in the customer-user list when I click "Customer User <-> Groups" so that I can add them to a group.  How can I get these people to appear on the list?   Does anybody know why these users are missing and how to correct it?  Thanks in advance. -Brian Klapchar