Subtotals (and autosums) don't change when you add a new row at the bottom of
the range. In both cases, the Excel function will generate a formula for
you, with a fixed range. If you add rows in the middle of the range, you get
automatic recalculation, but if you add a row at the bottom of the range, the
range doesn't expand. If you are subtotalling a table, you usually want to
add new rows at the bottom of each group, but to get the subtotals to work in
this case, you need to run the subtotal function again. And autosums work
the same way.

Excel has behaved this way for many versions, and I would have hoped it
would be fixed by now, but no !