Mysqli->ssl_set php accepting any string

Hi I have possibly the oddest thing ever, or maybe its the heat today.

I am trying to connect to a mysql instance with a user that was setup with "REQUIRE SSL"

The user works fine and using mysql from the linux command line everything works as expected.

Now when I use the code bellow, with the correct real_connect() params php connects to mysql even though I have passed junk into ssl_set()

$mysqli->ssl_set('asdad', null, null, null, null);

If I set ssl_set like so, or comment the line out

$mysqli->ssl_set('', null, null, null, null);

I get an ssl error as expected.

Any ideas on why it is allowing the ssl connection with a random string for the key? The docs say this is a file location?

$mysqli = mysqli_init();

$mysqli->ssl_set('asdad', null, null, null, null);

$connected = $mysqli->real_connect('HOST',
                                   'USER',
                                   'PASSWROD',
                                   'DATABASE',
                                   3306,
                                   null,
                                   MYSQLI_CLIENT_SSL);

EDIT 1:

I have tested this on 3 sperete machines and get the same probelm. I have tested on php5.3, php5.4 and php5.5

EDIT 2:

If I remove ssl_set completely and only set MYSQLI_CLIENT_SSL it still connects. Looks like there is a default cert OR it is not validating anthing.

UPDATE 1:

So I thought that it was because this is an RDS instance and AWS say this

These certificates are signed by a certificate authority. 

and therefore there was no need to set custom certs in php. However to prove this point I went back to the command line and tied

mysql -uUSER -pPASSWORD -hHOST --ssl

instead of

mysql -uUSER -pPASSWORD -hHOST --ssl_ca=mysql-ssl-ca-cert.pem

The first command does not work the second does work. Still very confused about what is going on here.