Im having the same problem. i dont understand why the purchase items bleed thru a assembly that is set to inseparable.
Are these parts you are creating or are you downloading them from the Internet?
Paul
If your CC items are bolts, nuts, etc. I would expect them to be set to 'Purchased'. If the CC items are structural steel shapes I would expect them to be set to 'Normal'. If you have a custom CC then you can set the Family Template to what ever works for your situation. If these assemblies are representing something that you need to show for design and illustration purposes only you should set them to 'Reference' this will exclude them from the BOM data for parts lists, structured or parts only.
If you can provide a screen capture and more information perhaps someone can provide more help. I have seen the BOM data behave in odd ways if a file becomes corrupt.
Paul