> The "g" stands for "git" and it's not part of the SHA1: 4ca117 are the
first six digits of the SHA1 at the HEAD of the branch

Ah, now that you spell it out, it's obvious. I swear I kept staring at the
git hash to find the "117" in "g4ca117" in
http://orgmode.org/cgit.cgi/org-mode.git/commit/?id=4ca1179c9e9c707267ac3738cc7c8442001b204b
but I never saw it! Now it stands out clear.

And of course, I should have realized that "g" can never be part of the hex
hash.

Thanks, and also thanks for confirming that you see this error too.