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.