Difference between pull --rebase and fetch+rebase

I have a branch configured to track a remote branch by rebasing. I excepted that "git pull" would therefore be equivalent to fetching from the remote repository followed by rebasing the remote branch, but it isn't. When doing "git rebase <remote>/<branch>", it applies only the commits after the merge base. When doing "git pull", it tries to apply two more commits (the two commits preceding the merge base). Why is this?

I get the same result even if I do "git pull --rebase <remote> <branch>", it doesn't seem to have anything to do with incorrect configuration of the branch.