git-send-email doesn't entirely understand --subject (or --in-reply-to)

I'm not absolutely sure this is git's fault but I tried to use the reply mechanism described here:

     https://public-inbox.org/git/20220718232843.151392-1-britton.kerin@gmail.com/#R

whic is to say this:

     git send-email \
         --in-reply-to=20220718232843.151392-1-britton.kerin@gmail.com \
         --to=britton.kerin@gmail.com \
         --cc=git@vger.kernel.org \
         --cc=gitster@pobox.com \
         --cc=newren@gmail.com \
         --subject='Re: BUG: git-check-ignore documentation doesn'\''t
come close to describing what it really does' \
         /path/to/YOUR_REPLY

and it failed like this:

$ git send-email --in-reply-to=xmqqtu7lc587.fsf@gitster.g --to=britton.kerin@gmail.com --subject='Re: BUG: git-check-ignore documentation doesn'\''t come close to describing what it really does' ~/my_reply_git_checkignore_bug_post /home/bkerin/my_reply_git_checkignore_bug_post No subject line in /home/bkerin/my_reply_git_checkignore_bug_post? at /usr/lib/git-core/git-send-email line 720.

Until I added this line to the top of /home/bkerin/my_reply_git_checkignore_bug_post:

     Subject: Re: BUG: git-check-ignore documentation doesn't come
close to describing what it really does

maybe this is normal but it seems weird given the presence of --in-reply-to and --subject and the fact that I didn't need to copy any other headers in.

Britton