This is a common problem that i have experienced with the default paypal mod. I found that if you manage to get it working PayPal IPN Mod is much less likely to have this problem as with the regular mod. OSC views any successful pass of a sale to PayPals website as a completed order with the regular PayPal mod. With PayPal IPN you get direct two way communication with paypals servers so OSC does not update the sale status till the sale is finalized on PayPals side. At least this is the expirence I have had hope it helps