TCP using IPv4-mapped IPv6 address as source

[Jonathan T. Leighton]

I've observed TCP using an IPv4-mapped IPv6 address as the source 
address, which I believe contradicts 
https://tools.ietf.org/html/rfc6890#page-14 (BCP 153). This occurs when 
an IPv6 TCP socket, bound to a local IPv4-mapped IPv6 address, attempts 
to connect to a remote IPv6 address. Presumable connect() should return 
EAFNOSUPPORT in this case. Please advise me if this is not to 
appropriate list to report this.

$ uname -a
Linux ubuntu 4.4.0-57-generic #78-Ubuntu SMP Fri Dec 9 23:50:32 UTC 2016 
x86_64 x86_64 x86_64 GNU/Linux

Best regards,
Jon