git log --shortstat doesn't respect -c (but --stat does)

This seems inconsistent:

$ git log --oneline --stat 91ccfb85176 -c 91ccfb8517 Merge branch 'sb/diff-color-move'

 diff.c                     | 28 +++++++++++++++-------------
 t/t4015-diff-whitespace.sh |  9 +++++++++
 2 files changed, 24 insertions(+), 13 deletions(-)
d1114d87c7 Merge branch 'js/rebase-i-final'

 sequencer.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
...

$ git log --oneline --shortstat 91ccfb85176 -c 91ccfb8517 Merge branch 'sb/diff-color-move'

d1114d87c7 Merge branch 'js/rebase-i-final'

4339c9f2df Merge branch 'jc/doc-checkout' ...

Especially since the manual for log -- shortstat says:

--shortstat
   Output only the last line of the --stat format containing total
   number of modified files, as well as number of added and deleted
   lines.