If I remember when you pay there is an option to pay after delivery, I bet your buyer has clicked this option. It might be worth in future asking buyers to use the pay now option or the item wont be released, its a bit like sending an item before a cheque clears.
These 21 day holds are normal and have been around for years. If you are a new seller or are selling a high risk item like an ipad, they will put the security hold on the payment. Only send the item by Special Delivery, enter tracking into Paypal and you'll receive the money when the guy leaves positive feedback or the 21 days is up. Make sure you post it on time as this will effect your account.
