Doctrine custom type always altering table

I have added a custom type like:

namespace My\SuperBundle\Types;

use Doctrine\DBAL\Types\Type;
use Doctrine\DBAL\Platforms\AbstractPlatform;

class Money extends Type
{
    const MONEY = 'money';

    public function getSqlDeclaration(
        array $fieldDeclaration,
        AbstractPlatform $platform
    ) {
        return 'DECIMAL(10,2)';
    }

    public function getName()
    {
        return self::MONEY;
    }
}

And in my application boot:

namespace My\SuperBundle;

use Doctrine\DBAL\Types\Type;
use My\SuperBundle\Types\Money;

class MyBSuperBundle extends Bundle
{
    public function boot()
    {
        //add custom quantity and wight types
        $em = $this->container->get('doctrine.orm.entity_manager');

        if(!Type::hasType(Money::MONEY)) {
            Type::addType(Money::MONEY, 'My\SuperBundle\Types\Money');
        }
    }
}

However every time I update the database with:

php app/console doctrine:schema:update --dump-sql

I keep getting the following:

ALTER TABLE product_price CHANGE price price DECIMAL(10,2) DEFAULT NULL

Apart from that everything works super fine. The fields in the DB are correct. Is there a reason why doctrine keeps updating with the same data?