git-whatchanged -<n>

Is this a bug in git-whatchanged, or at least an insufficiently
documented feature?

cd git

git whatchanged 837a156197e7~20..837a156197e7 -1 

    [nothing]

git whatchanged 837a156197e7~20..837a156197e7 -3

    [1 commit]

git whatchanged 837a156197e7~20..837a156197e7 -1 -m

    [1(?) commit]

It appears that without -m, merges are filtered after commits are
counted.