Cannot remove network interface card on provisioned resource manager VM

I cannot remove NIC to a already provisioned resource manager VM.

Powershell comands used give an error.

$vm = Get-AzureVM -ResourceGroupName dev-rg -Name dev-app01
Remove-AzureVMNetworkInterface -VM $vm -NetworkInterfaceIDs $vm.NetworkInterfaceIDs
Update-AzureVM -VM $vm -ResourceGroupName dev-rg

Debuged PShell:

Body:
{
  "error": {
    "code": "PropertyChangeNotAllowed",
    "target": "windowsConfiguration.additionalUnattendContent",
    "message": "Changing property 'windowsConfiguration.additionalUnattendContent' is not allowed."
  }
}

DEBUG: AzureQoSEvent: CmdletType - UpdateAzureVMCommand; IsSuccess - False; Duration - 00:05:02.4822503; Exception -
Microsoft.WindowsAzure.Commands.Common.ComputeCloudException: PropertyChangeNotAllowed: Changing property
'windowsConfiguration.additionalUnattendContent' is not allowed.
OperationID : '0d731ad8-f6e3-4150-bea9-532e79e2b09d' ---> Hyak.Common.CloudException: PropertyChangeNotAllowed:
Changing property 'windowsConfiguration.additionalUnattendContent' is not allowed.
   at Microsoft.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at Microsoft.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccess(Task task)
   at Microsoft.Azure.Management.Compute.VirtualMachineOperationsExtensions.CreateOrUpdate(IVirtualMachineOperations
operations, String resourceGroupName, VirtualMachine parameters)
   at Microsoft.Azure.Commands.Compute.UpdateAzureVMCommand.<ExecuteCmdlet>b__1()
   at Microsoft.Azure.Commands.Compute.ComputeClientBaseCmdlet.ExecuteClientAction(Action action)
   --- End of inner exception stack trace ---
   at Microsoft.Azure.Commands.Compute.ComputeClientBaseCmdlet.ExecuteClientAction(Action action)
   at Microsoft.Azure.Commands.Compute.UpdateAzureVMCommand.ExecuteCmdlet()
   at Microsoft.WindowsAzure.Commands.Utilities.Common.AzurePSCmdlet.ProcessRecord();
DEBUG: Finish sending metric.