Recent changes to the Pay Now button (Checkout process) on eBay have caused some PayPal buyers to unintentionally pay with their primary eBay address instead of their confirmed PayPal address. In many cases these addresses appeared to be identical, making the change hard to notice.

eBay recently changed the page that buyers are taken to when they use the Pay Now button from a completed listing. The new page allows them to select shipping addresses from their eBay account, as well as their stored addresses from their PayPal accounts.

Sellers are protected from chargebacks under PayPal's Seller Protection Program only if they sell to buyers' confirmed addresses. eBay acknowledged the problem again on its announcement board on Thursday. The company has added "strong messaging" to the Review Purchase page to indicate if an address is unconfirmed.

Sellers who received PayPal payments between 11/7 and 11/12 with unconfirmed addresses will be protected by PayPal's Seller Protection Program if the buyer had an identical address confirmed within their PayPal account. But it seems sellers affected by the change in the future will have no recourse if they don't notice a difference in eBay addresses and PayPal confirmed addresses.

http://pages.ebay.com/help/buy/payment-changes-FAQ.html