We have 'branch-1', with one commit. It is old branch, we also have Pull Request with this branch merged into 'master' by Stash.
After a time, someone add new commit into old 'branch-1' and open new Pull Request for this branch to 'master'.
At this time someone else merge pull request to master by other branch, e.q. 'branch-500'. And after this merge the pull request with branch 'branch-1' show 'remotely merge by Someone User' and close it. But master still not contains commits from this branch.