SCOM Cmdlet Add-SCOMRunAsAccount

I have one PowerShell script which creates simple Run As Account.

Script is as follows

Import-Module OperationsManager

$sSecureString = ConvertTo-SecureString "password" -AsPlainText -Force
$sCredentials = New-Object System.Management.Automation.PSCredential ("username", $sSecureString)
Add-SCOMRunAsAccount -Simple -Name "run_as_account_name" -Description "run_as_account_description" -RunAsCredential $sCredentials

Whenever username is say "username", run as account is created without no problem.

But whenever username is "username@domainname" or "domainname\username", run as account is created but domainname is removed from account name field.

I am not able to understand why "domainname" is removed.

This is creating problem to my integration.

Thanks,

Mukul