I just updated all my users to the latest build of spark (#609), and they are no longer able to see any room occupants. I found the only way to get this working now, is to enable "Anyone" to view the JIDs of room occupants. I came to this conclusion after i tested with an admin user, and a normal user (was trying to make sure it wasn't the packet filter).
the presense packets that are sent to a user who can't view JID of a user look like this
<presence id="hB2hJ-450" to="jared.go@onyx.net/Spark 2.6.3" from="incontact@ithelp.onyx.net/al.be">
<x xmlns="http://jabber.org/protocol/muc#user">
<item affiliation="none" role="participant">
<reason/>
<actor jid=""/>
</item>
</x>
</presence>
the presense packets for an admin user who CAN see JIDs
<presence id="hB2hJ-450" to="seth.go@onyx.net/Spark 2.6.3" from="incontact@ithelp.onyx.net/al.be">
<x xmlns="http://jabber.org/protocol/muc#user">
<item affiliation="none" jid="al.be@onyx.net/Spark 2.6.3" role="participant">
<reason/>
<actor jid=""/>
</item>
</x>
</presence>
I have a workaround, so this doesn't effect me, I'm just posting here in case something was "broken" in an attempt to fix something else. 
(sorry i'm not a programmer, hopefully this will be helpful to someone though)