I think this behavior is ok with commits that are in branches and with commits that were in branches that were force-updated (for a rebase, or a fix, or whatever reason). It keeps available the links to old version of a PR or something. (I sometimes do that. "The [first commit](link) does this, and the [second commit](link) does that." It's nice to be able to use the link after a few iterations of the PR.)
I'm not 100% sure if this behavior is fine for commits in PR that never were merged by the project. I guess it's an unavoidable bug/feature.
I don't like that this is posible with a commit that was never seen by the maintainer/developers/whatever of the project.
Technical question: Since all repositories are derived from the empty repository, then it is posible combine any user with any commit in GitHub? (To make it more believable it's probably better to use the same language of the project.)
