[Pacemaker] stopping resource stops others in colocation / order sets

[Phil Frost]

I'm sure this is a typical novice question, but I've been dancing around 
this problem for a day without any real progress, so could use some more 
experienced eyes. I'm setting up what must be a pretty normal NFS / DRBD 
/ LVM, 2 node, active / passive cluster. Everything works, mostly, but 
it doesn't quite behave as I'd expect, I'm not sure why, and not sure 
how to find out.

Start with the somewhat-contrived, but working test configuration which 
represents a DRBD device and some services (maybe a FS mount and Apache) 
that use it:

primitive drbd_nfsexports ocf:linbit:drbd \
         params drbd_resource="nfsexports" \
         op monitor interval="10s" role="Master" \
         op monitor interval="20s" role="Slave" \
         op start interval="0" timeout="240s" \
         op stop interval="0" timeout="100s"

primitive resB ocf:pacemaker:ping \
         params host_list="127.0.0.1" \
         op start interval="0" timeout="60s" \
         meta target-role="Started"

primitive resC ocf:pacemaker:ping \
         params host_list="127.0.0.1" \
         op start interval="0" timeout="60s" \
         meta target-role="Started"

ms drbd_nfsexports_ms drbd_nfsexports \
         meta master-max="1" master-node-max="1" clone-max="2" 
clone-node-max="1" notify="true" target-role="Master"

colocation colo inf: drbd_nfsexports_ms:Master resB resC

order ord inf: drbd_nfsexports_ms:promote resB resC

property $id="cib-bootstrap-options" \
         no-quorum-policy="ignore" \
         dc-version="1.1.7-ee0730e13d124c3d58f00016c3376a1de5323cff" \
         cluster-infrastructure="openais" \
         expected-quorum-votes="2" \
         stonith-enabled="false" \
         last-lrm-refresh="1339694844"

If resC is stopped

resource stop resC

then drbd_nfsexports is demoted, and resB and resC will stop. Why is 
that? I'd expect that resC, being listed last in both the colocation and 
order constraints, could be stopped without affecting the other 
resources. I've also found that if I construct a similar scenario with 
another ping as resA instead of the DRBD resource, it behaves as I'd expect.

Perhaps interestingly, if I delete the order constraint:

configure delete ord

the the DRBD resource says demoted, but resB starts. Maybe this is the 
issue to examine, because I can see how with the order constraint added, 
any demotion of the DRBD resource would lead to all the services being 
stopped.

So, what If I delete the constraint "colo", and replace it with what I 
understand to be equivalent (as I understand it, the order of the 
resources is reverse when there are only two. Confusing, but correct?):

configure delete colo
configure colocation colo1 inf: resC resB
configure colocation colo2 inf: resB drbd_nfsexports_ms:Master

Now just resC is stopped. Try making just resB stopped:

resource start resC
resource stop resB

now resC and resB are stopped, but I still have a DRBD master as I'd 
expect. Re-add the order constraint:

configure order ord inf: drbd_nfsexports_ms:promote resB resC

things remain unchanged.

What am I not understanding?