There is a bug if you enter 0.00 as the shipping cost for an order when doing
a manual invoice. If the shipping costs are set to 0.00 and then changes submitted,
the entered cost of 0.00 is removed and nothing is shown in its place. This is
not correct. It should be shown as 0.00 if I enter 0.00. If it is removed and
the box is turned back to blank, it looks like nothing has been entered when
it has.
It is not a big deal, but should be corrected. I assume the other boxes will
behave in similar ways.