Why can I submit more than one record in a one-to-one relationship?

I am using Laravel 5.2. Why can I submit more than one record in a one-to-one relationship? There are two tables, user and profile, and they have a one-to-one relationship.

User:

class User extends Authenticatable
{
    public function profile()
    {
        return $this->hasOne(Profile::class);
    }
}

Profile:

class Profile extends Model
{
    public function user()
    {
        return $this->belongsTo(User::class);
    }
}

I've setup the one-to-one relationship, but I can submit more than one record into table profile by one user account. Why is this?

via Chebli Mohamed