If the Attached card was Detached because the Top-Most Card changed zones from a board zone to a non-board zone, then the location that the Attached Card will Detach to is the last location the Top-Most Card was at before changing from a board zone to a non-board zone.
§ 435.4.b Core Rules PDF (officieel)
§ 435 Detach
§ 435.4 When a card Detaches from a Top-Most Card, its location is the same as the Top-Most Card from which it Detached.
