do i again need to buy a Return Ticket as i have L type Visa got from Shanghai Immigration office?

when i came to Shanghai from Pakistan i had to buy a RETURN ticket as i had visiting visa for 6 months to stay with my HUSBAND..i extended my visa from SHANGHAI EXIT ENTRY DEPT and i extend it every 3 months..im going back to PAKISTAN in july and will come back to Shanghai in SEPTEMBER.. if i get a SINGLE ENTRY VISA from Shanghai and i bought a one way ticket from here..when i will come back to Shanghai do i need to buy ANOTHER RETURN TICKET on this blue L type visa or can i just buy a ONE WAY TICKET from PAKISTAN??? plz help me. thanks a lot