reconfigureDvs_Task

I have scriptable task as follows (two inputs - vmhost VC:HostSystem & myDvs VC:VmwareDistributedVirtualSwitch):

dvsConfig = new VcDVSConfigSpec();

dvsConfig.configVersion = myDvs.config.configVersion;

hostMemConfigSpec = new VcDistributedVirtualSwitchHostMemberConfigSpec()

hostMemConfigSpec.operation = VcConfigSpecOperation.add;

hostMemConfigSpec.host = vmhost;

hostMemConfigSpec.backing = new VcDistributedVirtualSwitchHostMemberPnicBacking();

pnicSpec = new VcDistributedVirtualSwitchHostMemberPnicSpec();

pnicSpec.pnicDevice = "vmnic4";

hostMemConfigSpec.backing.pnicSpec = new Array();

hostMemConfigSpec.backing.pnicSpec.push(pnicSpec);

dvsConfig.host = new Array();

dvsConfig.host.push(hostMemConfigSpec);

myDvs.reconfigureDvs_Task(dvsConfig);

The task completes successfully but the host is not added to the dvs.  The pnicDevice (vmnic4) is not part of any dvs or vss.  Is there something I'm missing?

Thanks

Eric