We know that the money today is fiat currency, that it is money because the government says it's so. So when new money is printed or loaned out to the commercial banks by buying treasury bonds, government does not technically "owe" any thing. The only thing that is stopping it from creating new money every time need arises is the possibility of inflation.
Given all of that why is still money in circulation listed as a liability of the central bank? Am I missing something here?