Hi! Xun has found the source of the issue. But, I have to say this particularly modeling technique is troublesome in iAssembly and iPart. The issue is that iAssembly and iPart were designed to generate library components. Their definitions have to be specific and totally controlled by the author table (except custom iPart). Any inter-component dependency within iAssembly or iPart outside of the control of the author table will make such relationship brittle.
If you are trying to customize an assembly for different configuration purposes, you may want to consider using iLogic. The beauty of iLogic is that you are essentially working on the same set of files (iam and ipt). But, the geometry definitions can be changed by the logical rules in various levels. Once you are happy with a given setup, you can use iLogic Design Copy to create the dataset, separate from the source files.
Many thanks!
Johnson Shiue (johnson.shiue@autodesk.com)
Software Test Engineer