Do you have any idea on what might be causing this error in Drush w/ Drupal 7.2 (worked fine in Drupal 7.0)?

> Fatal error: Undefined class constant 'MYSQL_ATTR_USE_BUFFERED_QUERY' in /path/to/includes/database/mysql/database.inc on line 42  
> Drush command terminated abnormally due to an unrecoverable error.                                                                                                                    [error]
    Error: Undefined class constant 'MYSQL_ATTR_USE_BUFFERED_QUERY' in /path/to/includes/database/mysql/database.inc, line 42

Line 42 of database.inc contains the following line: 

    PDO::MYSQL_ATTR_USE_BUFFERED_QUERY => TRUE,

I thought this was related to PDO extension missing, but it is indeed installed. 

Here is the output of `drush -v -d status`:

>    drush -d -v status  
    Bootstrap to phase 0. [0.03 sec, 1.28 MB]                            [bootstrap]  
    Drush bootstrap phase : _drush_bootstrap_drush() [0.03 sec, 1.41 MB] [bootstrap]  
    Drush bootstrap phase : _drush_bootstrap_drupal_root() [0.07 sec, 3.18 MB] [bootstrap]  
    Initialized Drupal 7.2 root directory at /path/to [0.09 sec, 4.06 MB] [notice]  
    Drush bootstrap phase : _drush_bootstrap_drupal_site() [0.09 sec, 4.06 MB] [bootstrap]  
    Initialized Drupal site default at sites/default [0.09 sec, 4.06 MB] [notice]  
    Drush bootstrap phase : _drush_bootstrap_drupal_configuration() [0.09 sec, 4.06 MB] [bootstrap]
    
    Fatal error: Undefined class constant 'MYSQL_ATTR_USE_BUFFERED_QUERY' in /path/to/includes/database/mysql/database.inc on line 42
    Drush command terminated abnormally due to an unrecoverable error.                                                                                                                    [error]
    Error: Undefined class constant 'MYSQL_ATTR_USE_BUFFERED_QUERY' in /path/to/includes/database/mysql/database.inc, line 42 [0.1 sec, 4.56 MB]