DataObject seems to return content_length properly, but always return an empty value for bytes. Interestingly, using ObjectList produces a list of objects that return the proper value for bytes. I haven't determined why this works, but for an individual DataObject it does not. For the DataObject method, it seems like a potential solution to have content_length and bytes both return the same value, as the documentation describes, is to simply add another line in php-opencloud/lib/OpenCloud/ObjectStore/DataObject.php between the current lines 571 and 572 that does this:
$this->bytes = $value;
-Dan Emmons