Casting Desertion on MDFC raises error

[Alex-Vasile]

I cast the back side [[Birgi, God of Storytelling]] and opponent targets it with [[Desertion]]. On resolution we get this error:

[github-actions[bot]]

Birgi, God of Storytelling // Harnfel, Horn of Bounty - (Gatherer) (Scryfall) (EDHREC)

{2}{R} Legendary Creature — God 3/3 Whenever you cast a spell, add {R}. Until end of turn, you don't lose this mana as steps and phases end. Creatures you control can boast twice during each of your turns rather than once. :arrows_counterclockwise: {4}{R} Legendary Artifact Discard a card: Exile the top two cards of your library. You may play those cards this turn.

Desertion - (Gatherer) (Scryfall) (EDHREC)

{3}{U}{U} Instant Counter target spell. If an artifact or creature spell is countered this way, put that card onto the battlefield under your control instead of into its owner's graveyard.

[awjackson]

As of e40934921fcdb56f582567bd974761d3eb5a2444 this interaction no longer produces an error, but I'm not 100% sure which side of the MDFC is supposed to end up on the battlefield if a back-face spell is countered by Desertion.

712.9. By default, a resolving double-faced spell that becomes a permanent is put onto the battlefield with the same face up that was face up on the stack. Some abilities may cause a transforming double-faced spell with its front face up on the stack to enter the battlefield transformed.

712.10. A double-faced card put onto the battlefield from a zone other than the stack enters the battlefield with its front face up by default.

712.9 doesn't apply because the double-faced spell isn't "resolving", and 712.10 doesn't apply because the card isn't entering "from a zone other than the stack". I've gotten contradictory answers from judges as to what's supposed to happen, though most of the judges I've asked say the card should enter front-face up (currently in xmage it enters back-face up).