Schema API sensible to 'roles' column name

wamp running under vista
mysql 5.0.45
drupal 6.8
also on another testbed
wamp running under xp
mysql 5.0.51b
drupal 6.8

For my custom inhouse pilates.module, INSTALL file contains following hook_schema implementation
function pilates_schema() {
$schema['pilates_customer'] = array(
'description' => t('Stores Pilates customer account information'),
'fields' => array(
'customer_id' => array('type' => 'int','unsigned' => TRUE,'not null' => TRUE,'default' => 0,'description' => t("Customer uid.")),
'roles' => array('type' => 'text','size' => 'big','not null' => FALSE,'description' => t("Serialized user roles array.")),
),
'primary key' => array('customer_id'),
);

Get warning when installing module :
mysql_real_escape_string() expects parameter 1 to be string, array given in C:\wamp\www\pilates\includes
\database.mysql.inc on line 321.
MySQL tables actually got created anyway, but I still felt uncomfortable with.
Was able to get rid of warning only after changing column name 'roles' (for example to 'role')

Hope to have been of some help
Pavel