COUNTIF should count empty cells belonging to an array both as zero (0) and as
empty string (""). Therefore COUNTIF(<array>;0) and COUNTIF(<array>;"") should
yield the same results if the cells of <array> are empty (e.g. <array> {={||}}).
However, the upper left cell of the array is not counted as zero but is counted
as empty string, thus the results of both functions differ by one.

This problem was already observed before (see Issue 83917, last comment), but
not fixed at that time point. I initially encountered it in OOO310m19 but it is
still present in OOO320m12.