Bug: Misthollow Griffin should not be able to use it's alternative cast if facedown in exile

[Susucre]

Foretelling (with [[Ethereal Valkyrie]]) wrongly allow [[Misthollow Griffin]] to be cast using its own ability, although it is face-down.

Most relevant CR (no characteristics means the Griffin doesn't have its own cast ability active):

406.3a. A card exiled face down has no characteristics, but the spell or ability that exiled it may allow it to be played from exile. Unless that card is being cast face down (see rule 708.4), the card is turned face up just before the player announces that they are playing the card (see rule 601.2).

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Ethereal Valkyrie - (Gatherer) (Scryfall) (EDHREC)

{4}{W}{U} Creature — Spirit Angel 4/4 Flying Whenever Ethereal Valkyrie enters the battlefield or attacks, draw a card, then exile a card from your hand face down. It becomes foretold. Its foretell cost is its mana cost reduced by {2}. (On a later turn, you may cast it for its foretell cost, even if this creature has left the battlefield.)

Misthollow Griffin - (Gatherer) (Scryfall) (EDHREC)

{2}{U}{U} Creature — Griffin 3/3 Flying You may cast Misthollow Griffin from exile.

[Susucre]

Same with Hideaway (and any other exile face down effect)