Maybe I am wrong but if the USD loses .5% of its value and BTC exchange for the same number of USD, hasn't the BTC lost .5% of its value? If BTC maintained its value wouldn't BTC be worth .5% more USD than before? I don't see how anything can be priced independently of anything else as price is relative? Everything that can be bought is dependent on everything else that can be bought with that "currency" to determine its relative value I would think.
It seems to me that BTC either lost value, or the exchange value hasn't been adjusted due to exchange friction.
You are correct. They cannot be independent in the long run. As soon as there is real money to be made playing on these discrepancies, they will begin to disappear.