Error while calling Disconnect-IscsiTarget

Question

I have a Powershell script that attaches and detaches a Block Storage device.

The attachment follows this general sort of procedure:

1. Set-iScsiChapSecret
2. New-IscsiTargetPortal
3. Get-IscsiTargetPortal | Update-IscsiTargetPortal
4. Get-IscsiTarget | ForEach-Object { Connect-IscsiTarget }
5. Get-IscsiSession | ForEach-Object { Register-IscsiSession}

The detachment follows this general sort of steps:

1. Get-IscsiSession | ForEach-Object { Unregister-IScsiSession }
2. Get-IscsiTarget | ForEach-Object { Disconnect-IscsiTarget }
3. Get-IScsiTargetPortal | ForEach-Object { Remove-iScsiTargetPortal }

I am getting some very strange results. One of it is when I call Disconnect-IscsiTarget I get "The session cannot be logged out since a device on that session is current being used."

But I called the Unregister-IscsiSession and it seemed to work correctly.

Anyone seen this error and how I can fix it/find out more information?

Thanks