"T. Valko" wrote...
....
It's not just SUMPRODUCT, it's any array formula. Although you don't have
to array enter SUMPRODUCT it still calculates like an array entered
formula.
....

Overly broad, or would you like to take a stab at explaining why

=SUMPRODUCT(ROW(A:A))

returns 2147516416 (= 65537 * 32768) as expected?