This is a very big edge case, and I'm not even sure I would want this behavior changed.
I wanted to call coin of the realm after playing the final action in my hand so that I could hit 6 cards for magic lamp. The client never gave me the option -- it assumed since I had no actions in hand, I would never want to do this. This is a reasonable assumption 99% of the time. It's the same assumption made with crown.
In my game, I just undid to a prior action and called it then. However, I could imagine crazy situations where you're only going to play 1 action that turn and not being able to call the coin could prevent this.
That's one of the rare examples where you need to turn off Coin of the Realm smart autoplay to do what you want to. You can do so by rightlicking it somewhere (hand, supply, log,...).
Similarly, you can find some edge cases when you don't want Crown autoplay.
Oh, didn't think of the autoplay options. Makes sense -- thanks!