See [commit e46d56a9b4458370cb8de0c92e10688402749845](https://gitweb.torproject.org/tor.git/commitdiff/e46d56a9b4458370cb8de0c92e10688402749845). The behaviour described by the old version of that comment is probably correct; the behaviour implemented by that chunk of code (and described in the new version of that comment) is daft.