Long string fields are being silently changed to 255 characters in the schema

I have an entity like this:

/**
 * @orm:Entity
 */
class Product
{
    /**
     * @orm:Id
     * @orm:Column(name="Merchant",type="string",length=50)
     */
    protected $merchant;

    /**
     * @orm:Column(name="Name",type="string",length=500)
     */
    protected $name;
}

When I change the length of $name field to 4000 it updates the schema like it is supposed to:

php.exe -f console doctrine:schema:update --dump-sql
ALTER TABLE product CHANGE Name Name VARCHAR(4000) NOT NULL

But when I change the length to 5000 it just silently without any warning uses value 255 instead:

php.exe -f console doctrine:schema:update --dump-sql
ALTER TABLE product CHANGE Name Name VARCHAR(255) NOT NULL

I had to look into actual table definition using mysql browser to find this issue because doctrine doesn't even warn about it. This could lead to some pretty serious bugs!