When a host with a non-default port is in the ~/.ssh/known_hosts file then the
suggested command to remove it does not work.  For example, if known_hosts
contains:

  [192.168.42.129]:2222 ssh-rsa ....

then connecting with an outdated hostkey gives something like:

  Offending ECDSA key in /home/user/.ssh/known_hosts:440
  You can use following command to remove all keys for this IP:
  ssh-keygen -R 192.168.42.129 -f /home/user/.ssh/known_hosts

but that command doesn't do the right thing; it removes the entry for the
hostkey on the default port 22, not on port 2222.  The correct command to
suggest would have been:

  ssh-keygen -R [192.168.42.129]:2222 -f /home/user/.ssh/known_hosts

This is a resubmission of the upstream bug:

  https://bugzilla.mindrot.org/show_bug.cgi?id=2169

which was rightly resolved as INVALID because the bug actually comes from a
SUSE-specific patch:

 
https://build.opensuse.org/package/view_file/openSUSE:Leap:42.2/openssh/openssh-7.2p2-host_ident.patch?expand=1

The original source can be viewed here:

 
https://github.com/openssh/openssh-portable/blob/00df97ff68a49a756d4b977cd02283690f5dfa34/sshconnect.c#L1089