Here is Paypal's response. Still, not quite clear why hold was initialized a week after payment took place.
My guess is that payment was done from confirmed bank account, so Paypal considered that funds are clear before they got the money. As problems arise, they juts screw the seller. Which reminds me again, that Paypal can not be trusted as reliable payment service.
"Based on my review of you account, I could see that the transaction ID XXXXXXX was for your payment on January 7, 2009. The funding method for this transaction was instant transfer.
Transfers will be held as "Temporary Hold Placed" until the funds have cleared the bank and are received by PayPal. Once the transfer from the bank account is completed successfully, the payment type will post as "Temporary Hold Removed" and the funds will be credited to the PayPal account balance. Please allow 3-4 business days from the date the payment is initiated."