If you mean, when he import STEP file by opening .stp file, another body is created beside bodies from current STEP file.
At first, open step log file, and then you can check number of imported bodies.
ex) ! INFO- Total number of solids input for this translation : 1
If it is not same with bodies of result part file,
the step seed part maybe including existing bodies already. (although almost impossible)
Open and check .prt files in [%ugii_base_dir%\STEP203UG (or \STEP214UG)].