The problem is with paypal. I had a similiar situation few months back when I decied to sale my iPad on ebay.
The buyer even before he received the iPad filed a claimed with paypal that it was not delivered

Once I confirmed the delivery was made and provided paypal with the tracking number they finally released the funds to me.
After exactly 1 week I noticed there was another block on my account and my funds had been removed.
The buyer had the money back and kept the ipad. I called paypal like 100 times I was furious. They told me that paypal also requires a signature confirmation that the item was delivered (remember this is very important when selling on ebay, without it you are screwed) and I was responsible to pay back the 450$ to pay pal or they would contact a collection agency. I was at fault because there was no signature confirmation even after I explained to them that the package was picked up from the buyer at the post office and there was proof of that.
I told them that if they think I will sit back and let this buyer scam me and allow you guys to support this behaviour they got something else coming.
Not to brag but I am quite wealthy and I have a lot of time on my hands and with the help of my father I went after this idiots.
First thing I did was contact our lawyer who recommended us a good small litigation lawyer.
I also found the buyer contact number and called them up explaing to him that I was going to take legal actiong against him and paypal and I was about to contact RCMP and open an investigation.
MY lawyer sent a letter to paypal explaing what was going on and that the client was going to take legal action. Two days later paypal contact me and they tried to strong harm me telling me that if I didn't back down from this I would end up loosing a lot of money and pay theyr lawyers feees and blah blah
I proceeded to explain to them that if I have to waste 500K+ of lawyers fees to take you guys to court I will and I will not back down and next time contact my lawyer.
Now what happened is the funny part =) That imbecile of the buyer calls me back and tells me that miraculously he foudn the iPad and the neighbour had it this all time.
At this point my lawyer and I where literary pissing our pants for how hard we was laughing.
The buyer refunded my money that where originally given back to him from paypal and paypal tried to close the case.
Now what the buyer did is pretty much an admission of guilt and I would laugh at him try and produde that neighbour in court to testify that he held is iPad hostage for almost 2 months.
And paypal will be made to look like the idiots that they are.
At the moment I received an apology from paypal and they said they are going to refund me all the expenses of transfering the money to my bank account etc...
My lawyer said that is not enough we are looking for a little more then that.
Moral of the story stay away from paypal do anything in your power not to deal with them. If you sale on ebay never accept returns and try and have the buyer pick up the item.
Lot of people got screwed by paypal and had their funds hold for months at a time. The sad part is the vast majority of this people can not really afford good legal representation to go after this sharks and end up getting scrwed.
But once in a wile when you rip people off you gona run int he wrong guy and he will take action.
I can assure you that once I am done with paypal I will be going on a 10K shopping spree on ebay thanks to them.
Look what they did to this guy lol
http://www.youtube.com/watch?v=lr_7--e5A1g
I honestly feel sorry for him and I don't know how he can just sit there and do nothing.