Changing slot value in validate_$slotName seems to be creating multiple values for the slot

I need to do some correction in the slot value, because the slot value received from entities are not complete enough. I trying to update the slot value during validation of form in validate_$slotName function where i do return {“slot_name”: $slot_new_value} This seems to be working fine. When I run Rasa in interactive mode, I see rasa shows that slot has two values something like this

  You want Car Opening Set for which make model?                                                                            
  slot{"slot_name": "civic"}                                                                                               
  slot{"slot_name": "HONDA CIVIC"}                                                                                         
  slot{"requested_slot": "car_model_year"}  

I know I can improve slot capture using custom slot mapping, function extract_$slotName. My question is, what is the rasa interactive showing here, does it show history of slot values, or slots can keep multiple values in chronological order? Would be interested to know the shortfall of setting slot during validation, if any.

Thank you,