In the described workflow I came across another issue:
Is it true that TechDraw View isn't able to fully resolve relative positioning?
I createt an assembly with main and sub parts (first the 'classical' way - second started to rebuild it with Assembly 4 workbench). But in both cases the result is identical.
It is locically for me to set the 'z' property of the main part and to position subparts relative to the main part.
When I create a TechDraw View of the whole assembly all goes well.
The screenshot shows the result after changing the source of the view to solely 'MountingParts' to be shown ...