As far as Bitpay, that is BFL subcontracting out the actual exchange. It is just like using Paypal, or Mastercard, or Visa.
If I sent Paypal US$1000 to buy a TV direct from Sony. Then Paypal sends 80000 Yen to Sony (because they want to let Paypal handle the currency exchange) for my TV. When I ask Paypal for a refund 44 days later, will I get Yen or Dollars back? Will I get the same number of dollars I sent back? Or will it depend on the current exchange rate?
You will get a refund according to the price it was stated at. If the item was listed as costing 80000Yen, taht is what you get back, weather the dollar have gone up or down.
It's often that prices are denominated in one currency, but you can also see the price in other currencies aswell.
Here is a real-world example:
http://www.ebay.co.uk/itm/60-GH-s-Butterfly-Labs-Bitcoin-Miner-BitForce-Single-SC-ASIC-SEP-17-2012-/140999993104?pt=LH_DefaultDomain_0&hash=item20d4412710