Is it possible to move parts of a subassembly from within an assembly?

Following a new chapter from within my tutorial book I created a subassembly containing a screw, a washer and a nut.

I created mates in a way so to be able to shift the washer/nut combination.

After adding this subassembly to my major assembly, I don't seem to be able to shift the washer/nut combination anymore:

Is this by intention? Or am I doing something wrong here?

I was hoping to be able to create a mate in the major assembly that's supposed to be sticking the washer to the bottom part of the housing.