Well, I didn't. When my brother told me of the play, my first question was "are you sure?". My second question was "and blackjack plays 3-2? So I knew what blackjack played before I even even tested the game.
I probably should have looked at the rule screen, but I didn't and that is why I didn't initially know about the soft doubled when asked. But like I just explained almost any small unfavorable rule like no doubling soft hands was minuscule compared to the advantage of taking a second action after seeing your double down card.