When users create a ticket with an approver field they can not search for other users. As an administartor I obviously can.

When the user types the full username into the approver field Jira detects the user and sets it correctly but the searched username is not faded in.
All users have the global right to search users but they still can not search for them. Am I missing something?
All users, my admin as well are synced via LDAP with our Active Directory.
Thanks in advance.