沒遇過這種問題說~~
剛剛上了paypal查了一下..
應該是下列幾個問題..
==================================================================
What does a Status of Unclaimed mean?

A payment may be Unclaimed for one of the following reasons:

• Your recipient did not sign up with PayPal using the same email address that you used to send the money. The recipient simply needs to add this email address to his account (he can add up to eight addresses) and confirm the new email address. The money will then immediately appear in his balance.

• The recipient may not have confirmed his email address. Any payments sent to an account will not appear in the account balance until the user has completed the registration process by confirming his email address.

• The recipient must manually accept or deny this payment.

==================================================================
簡單的說..他可能跟登錄的email信箱不同, or可能未經過認證的email, or對方需手動接受/拒絕!!
不過用paypal如果將來有糾紛..只要您這邊顯示是Completed..交易仍有一定的保障在..