Panic over, Paypal have released my money back to me. It was all a bit weird - it seems he filed the claim the day before he signed for the parcel (which was about two weeks ago). Paypal never notified me and I just happened to notice tonight that my balance was lower than it should be. When I looked at my completed transactions, it said that my funds were on hold because of an unauthorised payment.
No sooner had I come here to ask for advice, by pure coincidence they gave me my money back! Oh well, one less thing to stress about!