A quick look in dev mode reveals the following SQL (mysql):

SELECT `hosts`.* FROM `hosts`
INNER JOIN `fact_values` fact_values_730703 ON (hosts.id = fact_values_730703.host_id)
INNER JOIN `fact_names` fact_names_730703 ON (fact_names_730703.id = fact_values_730703.fact_name_id)
INNER JOIN `fact_values` fact_values_804546 ON (hosts.id = fact_values_804546.host_id)
INNER JOIN `fact_names` fact_names_804546 ON (fact_names_804546.id = fact_values_804546.fact_name_id) WHERE ((fact_names_730703.`name` = 'operatingsystemrelease' AND fact_values_730703.`value` = BINARY '5.3') OR (fact_names_804546.`name` = 'operatingsystemrelease' AND fact_values_804546.`value` = BINARY '5.4')) ORDER BY `hosts`.`name` ASC LIMIT 0, 20

This should be:

SELECT `hosts`.* FROM `hosts`
INNER JOIN `fact_values` fact_values_730703 ON (hosts.id = fact_values_730703.host_id)
INNER JOIN `fact_names` fact_names_730703 ON (fact_names_730703.id = fact_values_730703.fact_name_id)
INNER JOIN `fact_values` fact_values_804546 ON (hosts.id = fact_values_804546.host_id)
INNER JOIN `fact_names` fact_names_804546 ON (fact_names_804546.id = fact_values_804546.fact_name_id)
WHERE
fact_names_730703.`name` = 'operatingsystemrelease'
AND
fact_names_804546.`name` = 'operatingsystemrelease'
AND
( fact_values_730703.`value` = BINARY '5.3' OR fact_values_804546.`value` = BINARY '5.4')

ORDER BY `hosts`.`name` ASC LIMIT 0, 20

This same principle applies for different fact names, as in the second example query.