Query that executes correctly in mysql client returns empty results in PHP / CodeIgniter

I am stuck trying to figure out why a query that works in mysql does not work in CodeIgniter. Here's the code:

    $this->db->select('*');
    $this->db->from('table');
    $this->db->where('table.project_id', $project_id);
    $this->db->where('table.user_id', $user_id);
    $q = $this->db->get();
    $result = $q->result();
    log_message('error', 'error message='.$this->db->_error_message());
    log_message('error', 'error number='.$this->db->_error_number());
    log_message('error', 'result='.print_r($result, true));
    log_message('error', 'last query='.$this->db->last_query());

The log output on this looks like this:

ERROR - 2013-09-20 08:53:03 --> error message=
ERROR - 2013-09-20 08:53:03 --> error number=0
ERROR - 2013-09-20 08:53:03 --> result=Array
(
)

ERROR - 2013-09-20 08:53:03 --> last query=SELECT `table`.*
FROM (`table`)
WHERE `table`.`project_id` =  '99'
AND `table`.`user_id` =  '1927'

When I run the query in mysql I get:

mysql> SELECT `table`.*
    -> FROM (`table`)
    -> WHERE `table`.`project_id` =  '99'
    -> AND `table`.`user_id` =  '1927';
+------+---------+----------+------------+----------------+
| id   | user_id | group_id | project_id | accepted_terms |
+------+---------+----------+------------+----------------+
| 2328 |    1927 |        8 |         99 |              0 |
+------+---------+----------+------------+----------------+
1 row in set (0.00 sec)

As you can see, the query that CI is constructing is valid, and it returns a result set in the mysql client. However, the query returns an empty Array in CodeIgniter. There are many, many other queries that are working on this page. I can't for the life of me figure out why this query isn't working in CodeIgniter?