hello
staff's user can see all his closed tickets (only tickets closed by him) on every department (not only his department) :
edit this file : include/class.staff.php
in function : getTicketsVisibility()
after this line : $visibility = Q::any(new Q(array('statusstate'=>'open', $assigned)));
add this line : $visibility->add ( Q::all(array('statusstate'=>'closed', 'staff_id' => $this->getId() )) );
work fine for me