[Git 2.9.2] diff inserted by commit.verbose not removed when rewording

I'm just a random Git user, not very familiar with the Git development process and so on, so please by gentle.

Setup:
- OS X 10.11.6
- Git 2.9.2 via Homebrew

Curiosity triggered me to enable 'commit.verbose' globally with 'git config --global commit.verbose true'. I have not configured it on the repo. It works as expected when committing; the diff is appended to the commit message template, yet doesn't make it into the commit when untouched. Today I noticed that when I then rebase interactively ('git rebase -i HEAD~2'; whatever) and reword a specific commit, the diff that is appended then is _not_ removed and _does_ make it into the commit. The template looks OK ('------------------------ >8 ------------------------' and so on is there) but it seems that the logic to actually cut along that line is not executed then.

I'm not sure what more I can say about it.