According to the DNS standard, hostnames with more than 63 characters per label (the sections between .) are not allowed [https://tools.ietf.org/html/rfc1035#section-2.3.1].

That said, enforcing that at the codec level might be the wrong choice. I threw together a quick patch moving the limits up to 250, and nothing blew up. It's unclear what the general usefulness of such a change would be, since DNS servers probably couldn't handle those requests anyway.

As for the original issue, if anybody is still doing something like that, could they provide a full example URL? I was unable to reproduce on HTTP (failed in a different place), or FTP.