I'm using PTC Creo Parametric 2.0, Build M150

I saved an assembly as a new copy, re-using the existing components. The assembly contained grouped parts and ungrouped parts. I added parts to the assembly and grouped the added parts. When grouped, the added parts disappear in the model. They are still listed in the model tree as active and unhidden, and searching through the layer tree didn't reveal any other evidence of what happened to them. Ungrouping the parts makes them re-appear. To continue exploring the matter, I ungrouped an existing group (for which the components were originally showing) and putting those into a new group caused those components to disappear as well.

Has anyone else had this problem? This is the first time I have seen this and have been able to successfully group parts in other assemblies. It is likely this assembly model was created in an earlier build of Creo 2.0.

Thanks for your thoughts!