Merging leaves repo in "still merging" state

After executing a merge as suggested in the docs, a git status suggests that "you are still merging".

Bash:

git init mergable
cd mergable
echo a > a
git add .
git commit -m "initial"
git switch -c mergy
echo b > b
git add b
git commit -m "additional"
git switch master
cd ..
git clone mergable mergable-clone

Python:

import pygit2
r = pygit2.Repository("mergable-clone")
mergy = r.references["refs/remotes/origin/mergy"]
parents = [r.head.target, mergy.target]
r.merge(mergy.target)

r.create_commit(
    "HEAD",
    pygit2.Signature("aaa", "mergy@merge.ch"),
    pygit2.Signature("aaa", "mergy@merge.ch"),
    "merge",
    r.index.write_tree(),
    parents
)

Bash:

cd mergable-clone
git status

Returns:

On branch master
Your branch is ahead of 'origin/master' by 2 commits.
  (use "git push" to publish your local commits)

All conflicts fixed but you are still merging.
  (use "git commit" to conclude merge)

Another git commit silences the message.

Reproduce the issue using the Bash and Python snippets, then inspect the r.merge and r.create_commit entry points and how they update merge state. Confirm the behavior with git status; done means the same commit flow no longer reports that the repository is still merging.