It seems that when you open the cards from the grimoire summary card on the far left the cards are not marked as read. It is only done so by moving the mouse over the stack of cards to the right and clicking on those that the red banner is removed and the card is marked as read. It took me some time to figure out why my cards were not being marked as read even though I was opening them. Hopefully can be fixed with a quick update as the functionality is probably tied to a click event listener on the cards to the right and not the icons in the summary card on the left.