On Mon, Feb 12, 2018 at 1:15 PM, Linus Torvalds
[off-list ref] wrote:

The reasoning is to avoid losing the signature from the tag (when
merging a signed tag, the signature gets inserted into the merge
commit itself - use "git log --show-signature" to see them).

I think the commit that actually introduced the behavior was

    fab47d057: merge: force edit and no-ff mode when merging a tag object

back in 2011, so we've had this behavior for a long time. So it's
probably not be worth tweaking the behavior any more, and maybe we
need to educate people to not update to other peoples state with "git
pull".

Maybe we could just tell people to have something like

       git config --global alias.update pull --ff-only

and use that for "try to update to upstream".

               Linus