We had almost exactly this happen to us last week where a buyre purchased 5-items and selected Express Post at checkout.

The system billed her for 5 lots of express when all 5 items would fit into a single package.

So we refunded her thru PayPal for the extra 4 she had paid for. $42.20

We were NOT issued (well not yet anyway) any defects for this paypal refund.

The only thing that has happened is that the FVF on the postage was charged at what she had originally paid rather than after we had refunded.

I called CS about it. They agreed and could see the problem and agreed to credit the FVFs so that we only paid on the one lot of Express Post fees.