Thanks to #1743, PRs are renamed to the merge commit title. However, that's typically an uninformative message, such as "Merge pull request #XXX from
Blaisorblade changed the title
Complete supporting guarded pDOT: Allow paths as value definitions, try 2Merge pull request #155 from Blaisorblade/path-defs-rebase-2
(I later renamed this back by hand).
Disabling sync-pr-commit-title fixes the problem. Unfortunately, I'm only merging PRs in a private repo, so I can't (yet) give a public link (but I should be able to, soon).

sync-pr-commit-title lets you disable the feature before merge:

You can just click cancel
Thanks for the answer; the real bug is the default title, but that isn't due to this extension.
GitHub proposes Merge pull request #XXX from ... as commit title, but only on some repos :-(.
Actually sync-pr-commit-title is made of two parts:
Merges...)So in this case it appears that the first part failed (so it remained Merges...) while the second part succeeded (so it set the PR title to Merges...)
If this behavior is reproducible, this is a bug somewhere here:
@Blaisorblade thank you for filing this issue. It helped me figure out what to disable to get rid of this annoyance.
@jsumners A request: has it occurred on a public repo? Can you post a link? All my examples are on a private repo 😕.
@Blaisorblade sorry, I am only seeing this in my private repos at the moment.
This just happened to me on a public repo if it helps: https://github.com/wagtail/vagrant-wagtail-develop/pull/24
This was the first time I used this feature (I’ve just installed the extension), I did notice the messaging announcing the change and offering to cancel, but thought I’d see what happens.
I can confirm that part 1. “First it copies the PR title to the PR commit title” (https://github.com/sindresorhus/refined-github/issues/2713#issuecomment-576419830) didn’t work – the PR commit was using the default merge commit wording.
I think @thibaudcolas' report is sufficient, but FWIW I've been running into this same thing multiple times (one example: https://github.com/azatoth/twinkle/pull/808). This is an awesome help, but simply clicking GH's merge button shouldn't default to something much less useful.
I've made a public repo just for it if that can help.
https://github.com/MathieuDerelle/refined-github-issue
(mode details in the closed (dupe) issue linked above)
https://github.com/jenkinsci/bom/pull/180 was also affected
I'll limit this feature to squashing commits.
Fixed. At some point we'll publish a new release. Currently we're still waiting for the Chrome Web Store to publish the last update.
Most helpful comment
I'll limit this feature to squashing commits.