Seems odd that there is even an argument. Patrick Harnett is supposed to have paid back some Bitcoins and has not. I am sure there are reasons for this but that still does mean he is in default. Paying back little bits of what he owes doesn't change that.
Did you read the thread you are responding to? The agreement by which he was supposed to have paid back some Bitcoins is not enforceable as agreed due to common mistake.
Or, do Bitcoins operate on a different set of logic?
Of course they do. Otherwise the agreement would be void because of the usurious interest rate.