Clone mean has to be a pure Clone, software can not have it's own input in Cloning.
Clone has to be Clone, Software can not over ride the Clone settings figures and taxes.
i also suggest that, 1 x 0 = 0 and 0 x 1 = 0 means some time in an estimate we need to keep items zero but need to show if you are buying the prices will be x, you should permit the same.
At the same time some time we are giving some items as free of cost and we need to just adjust our qty in our stock so in Estimate we might write item 1 qty 1 and prices = 0 and it has to accept and total should be zero.
Estimates should take care of both the things.