<tt>fossil co --latest</tt> gives you the latest leaf which is a descendant of your current checkout, and (as far as I can tell) has done so since <tt>--latest</tt> was introduced. This means that your test behaved as expected. But it is not what the help text says. I think that it is the help text that should change, since I don't think it is usually a good idea to change branches without asking explicitly.