It happens when you have built the body "off something else" , then NX will bring that "else" to the new component part.
Example.
1 I create a block.
2 draw a sketch on one of the faces of that block
3 extrude the sketch into a new body ( some distance away from the block)
4 export the extruded body to new component (= create new component and select the extruded body.)
Then in that new component file you will find the entire history as seen above since the extrusion is dependent of the sketch and the sketch (placement face) is dependent on the block.
If you instead create a non associative datum csys and place the sketch on that, you will not get the block in the new component.
Regards,
Tomas
The more you know about a subject, the more you know how little you know about that subject.