That's a known issue inside the IaaS API that the vRO plug-in uses to manage business groups through those business groups workflows. You don't have the same problem from the vRA UI because the UI (as per 6.x) doesn't use the same IaaS API to manage business groups.
The only alternative in 6.x for now is to use directly the generic entity manager helper from the plug-in itself. You can take a look at the first example from CRUD Infrastructure Administration Tasks Example Scripts.
I hope it helps.
OK, thanks for confirming that it is a known issue