That always happens, whichever menu you use, whichever choice you select. It's a part of Quest's core.
Maybe Alex can help you to remove it. You need to modify some functions and more advanced things.
DO NOT MODIFY THE CODE YOURSELF. WRONG CODING CAN CAUSE GAME ERRORS.And by the way... why a command like
sell shopkeeper 
? That's too...crazy. It can be something like
speak to shopkeeper,
tell shopkeeper about selling,
sell #object# to shopkeeper(althrough the latter may be a little hard.)