Although the idealized part is a CAD part, it is also an intermediary between the Master Part and the FEM. Components should not be added to it as if it were an assembly part.
Solution
Development locked out the ability to add component parts, via Assemblies Add Component, in NX 9.0 and later. It may be possible to add a component in NX 8.5 and earlier, but If an attempt is made in NX 9.0 or later, the following message should be displayed: A component cannot be added to Work Part
Notes