PowerCLI 5.1 problem - Set-VM "Index was outside the bounds of the array"

Hello,
We have a problem with vSphere PowerCLI 5.1 Release 1 build 793510.

We have a user - "test_user" in our vCenter Server to which we provide administrative permissions only on resource pool - "TestResourcePool".
We have a VM - "test-vm" under this resource pool.

Now we need to execute some simple commands from PowerCLI under "test_user".
We successfully connecting to vCenter server by "Connect-VIServer".
We successfully receive a list of VMs of "TestResourcePool" by "Get-VM".
But if we try to reconfigure VM, for example "Set-VM test-vm -NumCPU 1", we receive error: Set-VM "Index was outside the bounds of the array" At line:1 char:7 - FullyQualifiedErrorId : Core_BaseCmdlet_UnknownError,VMware.VimAutomation.ViCore.Cmdlets.Commands.SetVM.

While we can successfully reconfigure VM from Windows vSphere Client.

We found that if we provide any empty permission (create new role in vCenter and uncheck all privileges) for "test_user" on ESXi host level, then reconfiguring VM from PowerCLI completes successfully.

But we need that user has no permissions on ESXi host level and cannot see any information about host from Windows vSphere Client.

And if we execute "Set-VM test-vm -NumCPU 1" under user which have administrative permissions on whole vCenter Server, not only on certain resource pool, command completes successfully.

How can we resolve this issue?