The first component added to an assembly by my macro is fixed.

If there is a part already in the assembly then the first component my macro adds is not fixed.

It seems the first component added into an assembly is by default always fixed. That makes sense,  but is it an option that is set somewhere? How do I avoid the first component being fixed automatically?

When I create a new sub assembly in an assembly, the components in that new sub assembly are not fixed, even if there is only one, which actually often catches me out. So the application of 'first part always fixed in an assembly' is not 100%!