Calculated shipping for wrong amount?

We just sold an item, and the buyer paid immediately via PayPal. The problem is she only paid $4.00 for shipping and PayPal accepted it.

When we enter the ZIP codes on the listing in our Sold page, it calculates the correct amount ($9.83). We created an eBid invoice and that shows the shipping amount as $9.83 also.

I don't know if this is an eBid problem or a PayPal issue. Does PayPal allow someone to pay less than the calculated shipping amount? If not, did this incorrect amount get sent by eBid? Has anyone else had this happen?

Yes. I've had it happen. Twice.

Did you contact PayPal?

We sent an invoice (showing the correct shipping amount) to the buyer, asking for the additional amount. I have an uneasy feeling this is a PayPal issue, but I want to see what the buyer says before I talk to PayPal. I've heard they are playing games with eBay sellers, I hope they're not trying to do that with us.