Always DHCP gets assigned instead of Static ip pool in .net sdk 5.1

I am instantiating a vapp from template which has org network that is static ip pool. I am setting networkconfigtype as follows

networkConfigurationType.ParentNetwork = vdc.GetAvailableNetworkRefByName(orgNetwork);

//networkConfigurationType.

networkConfigurationType.FenceMode =FenceModeValuesType.BRIDGED.Value();

Once I power on the network is showing as DHCP instead of Static ip. I have spent 3 days on this to figure out whats wrong. No luck. Can some one help me how to do this programatically. I am using .net sdk 5.1version.

NOTE: Manualy if I assign network from hardware static ip pool gets selected automatically. Looks like its API issue.

Advance thanks

Sudheer