Is it common for imported STEP assembly files to have all the parts locked together?

I imported a mannikin as a STEP file and need the ability to re-position arms and legs. There are no assembly constraints between the body parts (as expected for STEP)
THE PROBLEM: I don't know how to make the parts movebale with respect to each other. The entire mannikin is moveable in the Master assembly, (Alibre 12.1)