SoftLayer_Billing_Item object mask failing for resourceTableId in SOAP/PHP

[rbraddes]

If I run the following code (where 62928835 is a valid billing item):

$object = \SoftLayer\SoapClient::getClient('SoftLayer_Billing_Item', 62928835, $apiUsername, $apiKey);
$result = $object->getObject();
print_r($result);

I can see [resourceTableId] => 315440 in the result. However, if I add an ObjectMask which includes resourceTableId:

$objectMask = "mask[resourceTableId]"
$object->setObjectMask($objectMask);

I get the following error:
Fatal error: Uncaught SoapFault exception: [SoftLayer_Exception_WebService_ObjectMask] Property 'resourceTableId' not valid for 'SoftLayer_Billing_Item'. in /Users/bradd/Documents/SoftLayer_Scripts/vendor/softlayer/softlayer-api-php-client/src/SoapClient.php:200

I can use the object mask in a REST call successfully (using a valid Billing Item ID).
https://api.softlayer.com/rest/v3/SoftLayer_Billing_Item/62928835/getObject.json?resultLimit=0,2&objectMask=resourceTableId