I don't think the reason phrase is optional, even though it can be just a whitespace. Even if I'm not mistaken, however, I don't see the reason for Guile not to be able to parse the status line without a space at the end.
Aside from that consider a string "HTTP/1.1 ", which should be a bad response because the status code should definitely be obligatory, however it passes through the (and d0 d1) check after applying this patch.
