PR timeline says “merged into master” when the actual target was a feature branch

[lsantire]

🏷️ Discussion Type

Bug

Body

Context

I observed an incorrect merge-destination label in a pull request timeline.

There were two dependent pull requests:

Pull request	Head branch	Base branch
Parent PR	A	master
Child PR	B	A

In other words, the child PR was intended to merge into A; only the parent PR targeted master.

Sequence that produced the issue

1. With both PRs open, locally check out branch A.
2. Merge branch B into A.
3. Also merge master into A.
4. Push branch A to the remote.
5. GitHub automatically marks the child PR (B → A) as merged.
6. Open the child PR and inspect its merge event in the timeline (here is where something wrong was observed, see details in sections below)

The relevant Git operations were equivalent to:

git switch A
git merge B
git merge master
git push origin A

These steps describe the observed incident. I have not independently reproduced the issue in a public test repository.

Actual behavior

The child PR's UI timeline displayed a message equivalent to:

user merged commit sha into master

However, the merge destination was branch A, not master.

At the time the message appeared:

• The parent PR (A → master) remained open.
• The child merge commit was not reachable from master.
• The child PR's base was still branch A.

Verification through the API

We checked both the PR metadata and its recorded merge event through GraphQL. The values below use the same generic branch names as the rest of this report.

Source	Reported merge target / base
UI merge timeline text	master
Merge event: MergedEvent.mergeRefName	A
Child PR: baseRefName	A

The historical merge event and the current PR base therefore agree with the actual feature-branch merge, while the UI names the default branch.

Expected behavior

The timeline should identify branch A as the merge destination, matching the recorded merge event.

Automatically marking the child PR merged is consistent with its changes having been merged into its base. The problem is the branch name displayed in that event.

Impact

The message incorrectly suggested that changes had landed in the protected default branch. We had to inspect the API and Git history to verify that no merge into master had occurred.

Related report

https://github.com/orgs/community/discussions/198570 describes a different PR timeline event displaying the wrong branch name. This may be useful context; I do not know whether the two reports share a cause.

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