If ssh/scp is used on computers with a shared home directory the localhost key noted in ~/.ssh/known_hosts is ambiguous. If the user fist ssh to localhost on host A and afterwards do the same on host B he is getting an error message. On the other side the host key for localhost is only a valuable security enhancement if localhost isn't bound to an uncommon ip number. (But this should cause a lot of troubles that hits a user before.)
$ man ssh_config [...] NoHostAuthenticationForLocalhost This option can be used if the home directory is shared across machines. In this case localhost will refer to a different machine on each of the machines and the user will get many warn- ings about changed host keys. However, this option disables host authentication for localhost. The argument to this keyword must be ``yes'' or ``no''. The default is to check the host key for localhost.
Move resolved bugs to CLOSED after 5.7 release