Navigating from VcDatastore to VcHostSystem

I'm developing a workflow that takes a VC:Datastore object as input and needs to locate one of the VcHostSystem's that has the datastore mounted, yet I am seeing some inconsistent results.

Taking the VcDatastore object, I can get the 'host' attribute which should return an array of VcDatastoreHostMount objects. I should then be able to take one of the VcDatastoreHostMount objects and pull the 'key' attribute from it to get a VcHostSystem. Whe I do this, the 'key' attribute comes back as null or undefined more often then not.

Has anyone seen this, or have suggestions for me?

Here's some pseudocode:

var allMounts = datastore.host;

if (allMounts.length > 0) {

   // get the first mount

   var hostMount=allMounts[0];

   if (hostMount.key==null) {

      throw("The hostMount key is null, cannot determine a host with this datastore mounted");

   }

}