Get-QADComputer and serialNumber

I am having a problem with obtaining the serialNumber attribute for computer objects in Active Directory using the Get-QADComputer cmdlet.

Using the following code, I get nothing back

Get-QADComputer -IncludeAllProperties OJR2UA0460YJP |fl serialNumber

However if I connect to the ARS service...

connect-QADService -proxy

Get-QADComputer -IncludeAllProperties OJR2UA0460YJP |fl serialNumber

It works and returns the contents of the serialNumber attribute.

Why won't the get-QADComputer cmdlet return the native attribute of serialNumber when connected to a domain controller?