Datetime field won't change on UPDATE in MySQL
I've set up a database and this is one of the tables:

    +-------------------------+------------+------+-----+---------------------+-------+
    | Field                   | Type       | Null | Key | Default             | Extra |
    +-------------------------+------------+------+-----+---------------------+-------+
    | id                      | char(23)   | NO   | PRI | NULL                |       | 
    | claim_date              | timestamp  | NO   |     | CURRENT_TIMESTAMP   |       | 
    | banned                  | tinyint(1) | NO   |     | NULL                |       | 
    | available_downloads     | tinyint(4) | NO   |     | 10                  |       | 
    | last_download_attempt   | datetime   | NO   |     | NULL                |       | 
    | last_activation_attempt | datetime   | NO   |     | NULL                |       | 
    | download_exp_date       | timestamp  | NO   |     | 0000-00-00 00:00:00 |       | 
    | available_activations   | tinyint(4) | NO   |     | 5                   |       | 
    | os_version              | tinyint(1) | NO   |     | NULL                |       | 
    +-------------------------+------------+------+-----+---------------------+-------+

The problem is: whenever I try to update a record with new values using both mysqli_stmt and mysqli->query() all values change apart from the datetime ones. 
The query I'm using is

    $stmt = $this->db->prepare('UPDATE licences SET available_activations=available_activations-1, last_activation_attempt=? WHERE id=?');
    $stmt->bind_param("ss", date("Y-m-d H:i:s"), $licence_id);
    $stmt->execute();
available_activations value decreases, but last_activation_attempt won't budge. I tried even to hardcode the time value (both in "Y-m-d H-i-s" and timestamp format), I tried changing the data type to timestamp, but it's still dead. When I enter the same query in mysql console it works fine, but php doesn't seem to handle it. What can I do in this case?
Datetime field won't change on UPDATE in MySQL
===

I've set up a database and this is one of the tables:

    +-------------------------+------------+------+-----+---------------------+-------+
    | Field                   | Type       | Null | Key | Default             | Extra |
    +-------------------------+------------+------+-----+---------------------+-------+
    | id                      | char(23)   | NO   | PRI | NULL                |       | 
    | claim_date              | timestamp  | NO   |     | CURRENT_TIMESTAMP   |       | 
    | banned                  | tinyint(1) | NO   |     | NULL                |       | 
    | available_downloads     | tinyint(4) | NO   |     | 10                  |       | 
    | last_download_attempt   | datetime   | NO   |     | NULL                |       | 
    | last_activation_attempt | datetime   | NO   |     | NULL                |       | 
    | download_exp_date       | timestamp  | NO   |     | 0000-00-00 00:00:00 |       | 
    | available_activations   | tinyint(4) | NO   |     | 5                   |       | 
    | os_version              | tinyint(1) | NO   |     | NULL                |       | 
    +-------------------------+------------+------+-----+---------------------+-------+

The problem is: whenever I try to update a record with new values using both mysqli_stmt and mysqli->query() all values change apart from the datetime ones. 
The query I'm using is

    $stmt = $this->db->prepare('UPDATE licences SET available_activations=available_activations-1, last_activation_attempt=? WHERE id=?');
    $stmt->bind_param("ss", date("Y-m-d H:i:s"), $licence_id);
    $stmt->execute();
available_activations value decreases, but last_activation_attempt won't budge. I tried even to hardcode the time value (both in "Y-m-d H-i-s" and timestamp format), I tried changing the data type to timestamp, but it's still dead. When I enter the same query in mysql console it works fine, but php doesn't seem to handle it. What can I do in this case?