hm... that sounds like they might be running into a SU group bug where group.entities.parent sometimes refer to the wrong definition.
V-Ray suffered from this, but I found a way to patch it.
@unknownuser said:
On the other hand if i explode the components and then turn the geometry into groups (actually when i want to do that i go fist inside the component, turn everything there into a group, get out of the component, and just then explode it because it's much moreeee faster exploding components into groups than to geometry) there's no problem. I guess that's maybe because groups are just geometry "grouped" and the components can have much more "properties".
From the API point of view groups and component instances both have a ComponentDefiniton, with very little difference.