The problem occurs under the following conditions:
Define a realm with the following realm configuration:
Top-level realm is amroot. A subrealm is example.com.
The subrealm example.com has two data stores: exampleDB and exampledminDB.
The data store exampleDB contains all the users starting at dc=example,dc=com. Supported LDAPv3 operations is set to user=read,write,create,delete,service.
The data store exampleadminDB contains an admin group for the realm. The admin group is DN: cn=example.com Realm Administrators,ou=Groups,dc=example,dc=com. This group has a single member, scarter. Supported LDAPv3 operations is set to group=read,write,create,delete.
Click the Subjects tab, then Groups, then the entry for example.com Realm Administrators.
Click the User tab.
All the users in the exampleDB data store show up as available, but scarter does not show up in the Selected field.
Workaround: Add the operation user=read to the supported LDAPv3 operations in the exampleadminDB data store.