PowerShell: setting security group

hi!
i'm trying to set the security group as follows but it is not reflected in the UI:

$securityGroup = Get-RDMSecurityGroup
$securityGroupGUID = [GUID]$securityGroup.ID
$sessions = Get-RDMSession
$sessionItem = $sessions[2]
Set-RDMSessionProperty -ID $sessionItem.ID -Property "SecurityGroup" -Value $securityGroupGUID

to verify i read the value using:

Get-RDMSessionProperty -ID $sessionItem.ID -Property SecurityGroup

and there the GUID is set ...

but when i right-click the entry in RDM (also after restarting RDM) the setting is not reflected.