Problem with left and right parenthesis in Sql query when use CodeIgniter Active record

[eluser]Berserk[/eluser]
Hi guys,
this is my problem:

+ i need get a blog post named: My Immortal (Band version)
+ when i use sql query in phpmyadmin, it returned result:

Code:

SELECT * FROM posts WHERE post_title =  "My Immortal (Band version)";

+ when i use CodeIgniter Active record to query it return no result ( NULL):

Code:

$this->db->where('title','My Immortal (Band version)');
         $query = $this->db->get('posts');
         $result = $query->result();

+ even when i use Active record to exec sql command it still return null:

Code:

$sql = 'SELECT * FROM posts WHERE post_title =  "My Immortal (Band version)"';
         $query = $this->db->query($sql);
         $result = $query->result();

I cant understand why it return null, is it a CI bug ?