Using the Select-Import cmdlet overwrites the WMI filter, even when the specific switch for it (-OverwriteWMIFilter) is not specified.
We have confirmed this issue as a Defect in GPOADmin version 5.20 and 5.21. The WMI filter on the target GPO for Select-Import should not be overwritten unless the -OverwriteWMIFilter switch is specified on the command line.
A Defect request was submitted to have this issue fixed in a future version of GPOADmin.
Defect ID 571228.