(Sorry if formatting is messed up as I'm replying from my phone.)
I think it makes sense to be forgiving here as this is something users will commonly configure. As long as it doesn't give inconsistent results (which doesn't seem to be the case) it is probably better to be liberal in what we accept. Also, if we change it now, user configurations will break without AFAICT a strong reason. So I'd tend to say keep what we have now.
IMO, we should still not document this just in case we find a strong reason to change it later. But we could perhaps add a unit test for this with a comment explaining why we try to accept this for the time being. Or we just do nothing and close the bug as wontfix.
Just my two cents.