> Thank you, James. The patch below fixes the problem and adds
> a test case based on your reproduction recipe.

Thank you, this also fixes my original use case.

FYI the reason this came up is that I was directly pulling changes from
a repository that could be considered a peer rather than upstream. The
commit histories had diverged and my next step was to create a merge
commit. I often use peer-to-peer operations like this to manage my
personal files.

-- 
James