Ticket owner's group
TicketOwnerGroup extend the restrict_owner option by setting a user group (or a list of user group or permission) of people to populate the owner combo box.
The list of groups or permissions is set by the restrict_owner_groups options :
[ticket] restrict_owner_groups = owners,TICKET_ADMIN
If you have any issues, create a new ticket.
[ticket] restrict_owner = yes restrict_owner_groups = owners,TRAC_ADMIN