I've installed a rhel 2 node cluster
I've added a vg resource (which of course is on a shared external lun) .

After halting the node which holds the VG the pcs status still shows me the resource is "stuck on the halted node.

We don't really have enough details to even guess. You don't tell us what version of RHEL, what kind of hardware, what kind of 'external LUN', how it's connected, how you're halting the node, cluster configuration, etc. Too many details to guess about. Please provide complete information, and we may be able to help.

But since this is RHEL...have you contacted Red Hat support? RHEL is a commercial, PAY FOR distribution, and when you pay for it, you get access to that support. Is your system patched from the Red Hat network, and up to date?