I have created a security group in my Computers OU and tested adding a couple of computers to it via Powershell. When I run Get-ADGroupMember against that group it returns the computer objects I would expect. However it does not return computers I have manually added through the AD Users and Computers application.
Also, when browsing the created group using AD Users and Computers I am not seeing the computers added via powershell, but do see computers added manually.
I feel like I may be missing something simple here...
The command I am using to add a computer is like so:
Add-ADGroupMember -identity S-1-5-21-1721530621-3416553010-47989647-1234 -members mycomputername$
To list group membership I am running:
get-adgroupmember -identity S-1-5-21-1721530621-3416553010-47989647-1342
OK. It's possible that you're talking to different domain controllers in your PowerShell session and in your AD Users and Computers console. (This would typically happen because PowerShell requires a domain controller running AD Web Services, and ADUC just uses LDAP.) You might just have to wait for AD replication to take place.