I am really struggling with this. Maybe I do not understand your reply.
I tried updating my powershell.exe.config with the connection string and membership stubs, as well as the full definitions added to the Dot.Net 4 machine.config file.
The user never gets added to the asp membership database using the new_spuser command in the same way it is listed by the OP. I have the same issue.
Are you asserting that if the Membership and Role provider config sections defining the FBA providers are properly added to the PowerShell config file that the command New-SPUser should add the user to the asp membership database in addition to defining the
user in SharePoint?