DOORS NG Requirement Owner list of users changes

We have CLM 6.0.1 users creating Requirements via the web and users with the same project permissions are seeing different lists of users to select in the Requirement Owner fields. They are using a mix of IE and Chrome browsers and the same user sees different lists of users depending on which web client they are using. Obviously they have the Add Users button to manually select a user to assign as the owner, but what is the logic behind the list of users that are listed by default? Is it a cache of recent users tagged by the user in that client, or a list of the users added to the project area or what?