(PHP) AdGroupCriterionService: UserListId's not listed for any CriterionUserList

I am trying to get userlist IDs that are associated with criterion for a specific adgroup. I am successfully able to retrieve all criterion for the adgroup, but according to the docs HERE there should be a UserListId returned in the CriterionUserList response object... However for all USER_LIST criterion the userListId is returned back as NULL (yet I can find it and navigate to it in the Web UI). Is there something I'm missing here? I can't think of any other services in the API that would give me what I want.

 object(CriterionUserList)#2488 (7) {

    ["userListId"]=>

    NULL

    ["userListName"]=>

    NULL

    ["userListMembershipStatus"]=>

    NULL

    ["id"]=>

    string(12) "xxxxxxxxx"

    ["type"]=>

    string(9) "USER_LIST"

    ["CriterionType"]=>

    string(17) "CriterionUserList"

    ["_parameterMap":"Criterion":private]=>

    array(1) {

      ["Criterion.Type"]=>

      string(13) "CriterionType"

    }

  }

Thanks!

--
--
=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~
Also find us on our blog and Google+:
https://googleadsdeveloper.blogspot.com/
https://plus.google.com/+GoogleAdsDevelopers/posts
=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~
 
You received this message because you are subscribed to the Google
Groups "AdWords API Forum" group.
To post to this group, send email to adwords-api@googlegroups.com
To unsubscribe from this group, send email to
adwords-api+unsubscribe@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/adwords-api?hl=en
---
You received this message because you are subscribed to the Google Groups "AdWords API Forum" group.
To unsubscribe from this group and stop receiving emails from it, send an email to adwords-api+unsubscribe@googlegroups.com.
Visit this group at https://groups.google.com/group/adwords-api.
To view this discussion on the web visit https://groups.google.com/d/msgid/adwords-api/e64f8540-caf5-4594-bd79-ce4e96b2f140%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.