All grants returns by node_access_records=
Array
(
    [0] => Array
        (
            [realm] => acl
            [gid] => 0
            [grant_view] => 0
            [grant_update] => 0
            [grant_delete] => 0
            [priority] => 0
            [#module] => acl
        )

    [1] => Array
        (
            [realm] => acl
            [gid] => 0
            [grant_view] => 0
            [grant_update] => 0
            [grant_delete] => 0
            [priority] => 0
            [#module] => acl
        )

    [2] => Array
        (
            [realm] => acl
            [gid] => 0
            [grant_view] => 0
            [grant_update] => 0
            [grant_delete] => 0
            [priority] => 0
            [#module] => acl
        )

    [3] => Array
        (
            [#module] => content_access
        )

    [4] => Array
        (
            [#module] => content_access
        )

    [5] => Array
        (
            [#module] => content_access
        )

    [6] => Array
        (
            [grant_view] => 1
            [grant_update] => 1
            [grant_delete] => 1
            [realm] => content_access_rid
            [gid] => 5
            [priority] => 0
            [#module] => content_access
        )

    [7] => Array
        (
            [grant_view] => 1
            [grant_update] => 1
            [grant_delete] => 0
            [realm] => content_access_rid
            [gid] => 4
            [priority] => 0
            [#module] => content_access
        )

    [8] => Array
        (
            [grant_view] => 1
            [grant_update] => 1
            [grant_delete] => 1
            [realm] => content_access_rid
            [gid] => 6
            [priority] => 0
            [#module] => content_access
        )

    [all] => Array
        (
            [realm] => all
            [gid] => 0
            [grant_view] => 1
            [grant_update] => 0
            [grant_delete] => 0
            [priority] => 0
            [#module] => content_access
        )

)

so Im guessing the rows below that have 
    [#module] => content_access
    [priority] => –
are the ones that are bringing over this empty set? not sure why, but thought could help debug		

$acquired_grants_nid[]=Array
(
    [realm] => acl
    [gid] => 0
    [grant_view] => 0
    [grant_update] => 0
    [grant_delete] => 0
    [priority] => 0
    [#module] => acl
)
</li>
  <li>$acquired_grants_nid[]=Array
(
    [realm] => acl
    [gid] => 0
    [grant_view] => 0
    [grant_update] => 0
    [grant_delete] => 0
    [priority] => 0
    [#module] => acl
)
</li>
  <li>$acquired_grants_nid[]=Array
(
    [realm] => acl
    [gid] => 0
    [grant_view] => 0
    [grant_update] => 0
    [grant_delete] => 0
    [priority] => 0
    [#module] => acl
)
</li>
  <li>$acquired_grants_nid[]=Array
(
    [#module] => content_access
    [priority] => &ndash;
)
</li>
  <li>$acquired_grants_nid[]=Array
(
    [#module] => content_access
    [priority] => &ndash;
)
</li>
  <li>$acquired_grants_nid[]=Array
(
    [#module] => content_access
    [priority] => &ndash;
)
</li>
  <li>$acquired_grants_nid[]=Array
(
    [grant_view] => 1
    [grant_update] => 1
    [grant_delete] => 1
    [realm] => content_access_rid
    [gid] => 5
    [priority] => 0
    [#module] => content_access
)
</li>
  <li>$acquired_grants_nid[]=Array
(
    [grant_view] => 1
    [grant_update] => 1
    [grant_delete] => 0
    [realm] => content_access_rid
    [gid] => 4
    [priority] => 0
    [#module] => content_access
)
</li>
  <li>$acquired_grants_nid[]=Array
(
    [grant_view] => 1
    [grant_update] => 1
    [grant_delete] => 1
    [realm] => content_access_rid
    [gid] => 6
    [priority] => 0
    [#module] => content_access
)
</li>
  <li>$acquired_grants_nid[]=Array
(
    [realm] => all
    [gid] => 0
    [grant_view] => 1
    [grant_update] => 0
    [grant_delete] => 0
    [priority] => 0
    [#module] => content_access
)
</li>