Quite right. My bad. Sometimes my focus is not so good.
EH Ref Guide pg 5 wrote:
^ Whenever a card is discarded, it is placed in a faceup discard pile by its deck.
^ Double-sided cards, such as Spells or Conditions, are immediately shuffled back into their respective decks when discarded.
^ When an investigator searches a deck for a specific card and does not find the card he is looking for, he also searches that deck’s discard pile.
^ When a deck of cards is empty, immediately shuffle its discard pile to form a new deck. The Mythos deck is never replenished.
EH Ref Guide pg 10 wrote:
^ When an investigator searches for a card, he looks at cards from the bottom of the deck until he finds a card that matches his search criteria.
^ If an investigator does not find a card that matches his search criteria while searching a deck, he then searches that deck’s discard pile.
^ After a deck is searched, the investigator shuffles that deck.
So the discard is only shuffled in when the deck is empty.