Out of sync auto increment MYSQL

Question

I have a weird behavior on one of the tables I am working with, I am not sure if it is my php code or some setting on the database that is causing auto incremented id's to fall out of sync.

If I run the following code without any indexes on name&cars I get:

    $cars = array("Volvo","BMW","Toyota");
    $name = "John Smith";

        foreach($cars as $value)
        {
                try 
                {

                 //insert into database with a prepared statement

                   $query = $db->prepare(
                   'INSERT INTO cars (name,cars) 
                   VALUES (:name,:cars) 
                   ');
                   $query->execute(array(           
                   ':name' => $name,
                   ':cars' => $value
                   ));

                }
                //else catch the exception and show the error.
                catch(PDOException $e) 
                {
                    $error[] = $e->getMessage();
                }   
        }

///Results
id || name       || cars
1  || John Smith || Volvo
2  || John Smith || BMW
3  || John Smith || Toyota

But if I put an unique index on name&cars, the auto increment gets out of sync and I can't understand why because I can't see anything wrong with my PHP code?

$cars = array("Volvo","BMW","Toyota");
    $name = "John Smith";

        foreach($cars as $value)
        {
                try 
                {

                 //insert into database with a prepared statement

                   $query = $db->prepare(
                   'INSERT INTO cars (name,cars) 
                   VALUES (:name,:cars) 
                   ');
                   $query->execute(array(           
                   ':name' => $name,
                   ':cars' => $value
                   ));

                }
                //else catch the exception and show the error.
                catch(PDOException $e) 
                {
                    $error[] = $e->getMessage();
                }   
        }

///Results
id || name       || cars
3  || John Smith || Toyota
1  || John Smith || Volvo
2  || John Smith || BMW

Answer 1

Why do you think, it's out of sync? John's Toyota has still id 3 and his Volvo is 1.

How do you get your results? You are just SELECTing your cars, right? The behaviour is fine, because there is no need to order the data by the id without any ORDER BY statement.

You should query with SELECT id, name, cars FROM cars ORDER BY id ASC.

It's totally okay with mysql that an unordered list is returned. The "unorder" is just the result of some internal optimization.