If you look in
J. J. Dongarra, J. Du Croz, S. Hammarling, and R. J. Hanson,
An extended set of FORTRAN Basic Linear Algebra Subprograms,
ACM Trans. Math. Soft., 14 (1988), pp. 1--17.
which is where the specifications for the Level 2 BLAS are defined, you
find in Section 4 (Argument Conventions)
"Note that it is permissible to call the routines with M or N = 0,
in which case the routines exit immediately without referencing
their vector or matrix arguments."
So, actually the implementations you have tested are all correct.
I shall suggest that the man pages make this explicit.