change quantity after mark as complete

Thank you for implementing the new quantity feature. IMHO this is helpful for trading and price history. However there is one drawback, which is that you cannot correct the value after you have marked a trade as complete. Since the field for the quantity is further down, it can happen that you forget to set it to the correct value. E.g. you list 40 perfect amethysts but then trade only 20 and forget to change the amount before marking as complete. Then it is no longer possible to change the quantity. However it is still possible to correct the amount and the type that the buyer paid. I would like to be also able to change the quantity afterwards in case of such an error.