For example this one: https://github.com/angular/angular.js/pull/8, The commit list in the pull request is empty.
However, when I mine the repository's commit history, I can find commits related to this pull request. They are commited by the same person as the one who open the pull request, and have very similar commit message as the pull request statement.
I want to know what could cause an empty commit list in the pull request.
Also, many pull requests in this repository are not merged, but the actual commit can still be found in the commit history (different hash, but same content, same commit message and same authtor/committer). What could cause this? A force push to the remote repository?