Is "2001::0:8080" 2001::0 port 8080, or 2001::0:8080 port 80? There you go. Of course you can argue for automatic conversion when there's no ambiguity.
It's 2001::0:8080 port 80. Require the brackets for specifying a port number with a v6 address, and don't accept a port without the brackets. That way there's no ambiguity.
