In fn layout::parser::font, there is a long list of else ifs, including the following two:

} else if token.eq_ignore_ascii_case("normal") {
    weight = FontWeight::Normal;
}

and

} else if token.eq_ignore_ascii_case("normal") {
    stretch = FontStretch::Normal;
}

which both have the same condition, so the second one cannot be reached (source code).
I don't know what the intended behavior would be.