Karn Liberated (Vanguard)'s -3 ability not exiling card from Greg's hand [Investigating]

biosterous

Ability text: "Exile the first card without mana from your opponent's hand. Then: [etc, second part of the ability functions fine]"

It is currently behaving as if the text was "If your opponent's first card has no mana, exile it from their hand. Then: [etc]"

To reproduce: Greg's first card has 1 or more mana, Greg has at least one card with zero mana. Use Karn Liberated's -3 ability.

Expected behaviour: Greg's first card has mana, and is not exiled. Ability checks next card (until it finds a card without mana). [Second, third, whatever] card has zero mana and is exiled. Ability moves on to the second part.

Observed behaviour: Greg's first card has mana, and is not exiled. First part of the ability ends. Ability moves on to the second part.