Go into the Kick case for the clan command and add this 

If you invite a player who already is in a clan, and /clan kick them, it kicks them out of their own clan.

var kickPlayerUserId = kickPlayer.UserIDString;
if (!myClan.IsMember(kickPlayerUserId) && !myClan.IsInvited(kickPlayerUserId)) {
sb.Append(_("This player is not a member of your clan:") + " " + kickPlayer.displayName);
break;
}
if (myClan.IsInvited(kickPlayerUserId))
{
sb.Append(_("This player is not a member of your clan:") + " " + kickPlayer.displayName);
break;
}