I find this a bit naughty by eBay.
Had someone buy 20 magazines off me, all separate auctions, and pay before I could send amended payment details to show combined postage. I refunded him about 90% of what he'd paid for postage.
What he has paid me is pending for 14 days or until delivery can be verified but the refund I sent him has come straight of my available funds and not the pending funds. Not too happy about this as I had intended to use the available funds to buy a couple of items but now I have a negative available balance.