User's OG permissions are taking precedence over Node Access User Reference grants. Is that how it's supposed to work?

I configured the Node Access User Reference module to grant View rights to selected members in a group. I created a node of type Group Post so only members of that group can see that node. Now, editing that node, I'm trying to limit which users within that group may see it. With the Node Access User Reference field, I've checked the boxes of a few select group members while leaving other members' boxes unchecked. Then I saved that page. The problem is that all of the group's members can still see the node. It's as if nothing ever happened. On the DB end though, I see the row in node_access that links the Group to the Group's post is gone and the content_ref_field table has three new rows for each person (whose name I placed a checkmark next to).

So my questions are....Does an unchecked box imply removal of all Grants related to that node?
Are user's OG permissions supposed to take precedence over Node Access User Reference grants or have I done something wrong?

thanks