game #36696925 on frankfurt
Turn 10. Citadel already in effect.
Player chose "Crown", intended as a treasure, effect was doubled, despite that it was played as a treasure.
That is correct behaviour:
The important thing to note is that you don't "play Crown as Treasure" (or "as Action"). You're playing an "Action-Treasure" in your buy phase (and you can do that because it's a Treasure). If that also happens to be the first "Action" that you play in this turn, it gets doubled by Citadel.