Hermit, I really don't know. I always thought that debit cards worked as credit only to the limit of funds available.
I know just linking a card that appears to be a credit card to Paypal allows instant payments. You should be able to buy stuff over $1000 in Paypal if you have it linked to your bank account and linking a credit card will make the payment instant no matter what the amount is you are trying to withdraw.
If you have funds in your debit account of say, $2500, you are able via the credit card option to use it to buy goods up to $2500. That's how those debit cards you load up to take overseas work. You have credit to the value of the money loaded up against the card. If you try to buy through paypal using the attached debit as a credit, I woukd imagine, like any other vendor Paypal would check the available balance and pay it. Have you asked Paypal?