Description:
------------
It seems that the \mysqli->connect_error and \mysqli->connect_errno values (when using mysqli in the object-oriented mode) shares state between all connections. This is not documented (it should at least have a warning in the documentation).

When running the example code (make sure you point the first and last connection to a valid MySQL server) i found that all connections reported no errors, although the second one failed. Sometimes (although I'm having a hard time reliably reproducing this) i'm pretty sure i've also seen all three connections report errors (although the third and last connection succeeded). Maybe this value is not overwritten when a successful connection is done, in all code paths?

Either way, i think this should be either documented or fixed - as one would not expect this information to be shared between instances when the syntax doesn't indicate that. If this is a static property, i would expect the documentation said to use \mysqli::$connect_error, but that doesn't even work.   

Test script:
---------------
$connections = array(
    'Valid connection' =>   new mysqli('127.0.0.1', 'root', '', 'test', 3306),
    'Invalid connection' => @new mysqli('127.0.0.1', 'root', '', 'test', 3307),
    'Valid connection 2' => new mysqli('127.0.0.1', 'root', '', 'test', 3306),
);

foreach($connections as $desc => $conn) {
    echo "$desc:\n".
        "connect_error = ".$conn->connect_error."\n".
        "connect_errno = ".$conn->connect_errno."\n".
        "ping =          ".@$conn->ping()."\n\n".
}


Expected result:
----------------
Valid connection:
connect_error =
connect_errno = 0
ping =          1

Invalid connection:
connect_error = Connection refused
connect_errno = 2002
ping =          

Valid connection 2:
connect_error = 
connect_errno = 0
ping =          1

Actual result:
--------------
Valid connection:
connect_error = 
connect_errno = 0
ping =          1

Invalid connection:
connect_error = 
connect_errno = 0
ping =             

Valid connection 2:
connect_error = 
connect_errno = 0
ping =          1