Too late to edit, but I realize the problem is more likely to come up in the face of sudden and significant deflation, which isn't something we see in other currencies terribly often.
Surprisingly wide swings in fiat currency value can happen over the course of a month or two though. I imagine the volatility of BTC might cause problems for things like pre-orders.
I once placed a large order with a US company; unfortunately the order couldn't be filled for about two months.
I really wish they had billed me up front, because by the time they did bill me, the order cost 30% more in NZD.
While that's not quite the situation in question (you took my money and now I want a refund is stickier than "I want to pay you now rather than later" - in your case, you could always just cancel your order...), it's still relevant in that things could well have been reversed and (the bit I overlooked in my second comment) a rapid inflation in one currency looks a lot like a rapid deflation in others if you hold the inflating currency.
