Bitcoin is NOT a currency!
In it's simplest form it is just payment rails. Stop thinking about is as currency and what is left to regulate?
If a merchant selling a pair of jeans for $250 accepts a 1 bitcoin and customer 2 weeks later asks for a refund with a value of a bitcoin going up to $300. Is he going to get 1 bitcoin back or a value of the jeans he bought? Naturally, the value, which means 3/4 of a bitcoin at the time of the refund. So, how does it make bitcoin a currency. ITS NOT!
What do you think?
Well, that depends on in what currency the merchant denominated that jeans. If that was $250 but as an alternative payment method he/she accepted 1 BTC (at the then current $250 exchange rate) then he should refund $250 worth BTC. If he sold that Jeans for 1 BTC what was worth $250 in that time then he/she should give back 1 BTC even if it went up to $300 in the meantime.