`validate_my_slot()` skipped on slot autofill in a form

Rasa Open Source
1

My slots and form are as:

entities:
- email

slots:
  user_email:
    type: text
    influence_conversation: false
    mappings:
      - type: from_entity
        entity: email
        conditions:
          - active_loop: login_form
forms:
  login_form:
    required_slots:
      - user_email

And my validate_form action:

class ValidateLoginForm(FormValidationAction):
    def name(self) -> Text:
        return "validate_login_form"

    async def validate_user_email(
            self,
            slot_value: Any,
            dispatcher: CollectingDispatcher,
            tracker: Tracker,
            domain: Dict
    ) -> Dict[Text, Any]:
        if tracker.get_slot(REQUESTED_SLOT) == USER_EMAIL:
            # email validation logic
            if valid_email:
                return {USER_EMAIL: slot_value}
            else:
                dispatcher.utter_message(response="utter_unregistered_email")
                return {USER_EMAIL: None}
        return {USER_EMAIL: tracker.get_slot(USER_EMAIL)}

And now while testing below are 2 cases: #Case1 (Proper functioning)

>> /login
Bot works fine and asks for email
>> put invalid email
Bot works fine and tells its invalid email & asks to put email again

#Case2 (Abnormally skipping validation)

>> /login{{"email":"invalid_email"}}
Bot doesnt run validate_user_email() and thus accepts invalid email as slot value
Bot continues the form

Why is validate_user_email() being skipped in the second case? Isnt it supoposed to run everytime that specific slot is being filled, irrespective of how it is filled?