Description of URI.parseServerAuthority contains phrase:

" This method is provided because the generic URI syntax specified in RFC 3986 cannot always distinguish a malformed server-based authority from a legitimate registry-based authority. It must therefore treat some instances of the former as instances of the latter. The authority component in the URI string "//foo:bar", for example, is not a legal server-based authority but it is legal as a registry-based authority."

Example above is wrong. Host name can't contain ':' symbol. (Now ':' is a memeber of 'gen-delims').

It seems that a malformed server-based authority can't be a valid registry-based authority now.
(RFC 3986 page 55: Registry-based naming authorities that use the generic syntax are now defined within the host rule.) => valid reg-based IS valid host IS valid server-based