Remove-VM -DeletePermanently leaves files behind

I'm removing a VM with the -DeletePermanently switch but it's leaving a few files around.

I've tried:

$oldVM = Get-VM -Name $vmName

Get-HardDisk -VM $oldVM | Remove-HardDisk -DeletePermanently -Confirm:$false

Remove-VM -VM $oldVM -Confirm:$false

And:

Remove-VM -VM $vmName -DeletePermanently -Confirm:$false

In either case the VM is removed from inventory but the folder on the DataStore remains with a few small files. Some nvram, vmx vmxf, vmsd and log files remain - all very small (< 10KB).

Any idea why this is happening?

Thanks in advance.

Steve