Effective May 7th, 2019
"We're changing how we treat refunds. If you refund (partially or fully) a transaction to a buyer or a donation to a donor, there are no fees to make the refund, but the fees you originally paid as the seller will not be returned to you."
In other words, the 2.9% fee from the original transaction will no longer be refunded (as well as the original 30ยข, which they've always kept).
See full notification about this and other changes at:
https://www.paypal.com/us/webapps/mpp/ua/upcoming-policies-fullFrom what I've seen, several eBay sellers are already talking about jumping ship because of this.