Dave,
Why wouldn't you speak up if you know a mistake is about to be made?
As I explained in the other thread, at least twice, speaking up only once it is my turn to act gives me a slight advantage.
In general, if a player is about to make a mistake, I want to give him that opportunity, so that I can get a better read on his intentions. Not correcting the mistake, gives me a better read on the next player, etc.
And, in a somewhat abstract way, any player who says anything while there is action pending to another player, could be violating the "don't talk about the hand during the hand" rule, and/or the "one person to a hand" rule.
Must a player speak up if his bet is misinterpreted and action follows? I say no.
I feel that a player has an obligation to protect their actions.
This includes ensuring that their bets and raises are clear and understandable.
Anytime a player decides to not adhere to this philosophy, they leave the decision up to the TD as to what their action is. They shouldn't be surprised nor upset when they don't agree with the TD's interpretation. They had every chance available to them to be clear as to what their action was, yet made the choice not to.
I also mentioned this in the other thread: What if the player in question didn't realize there was a mistake until the action came back to him?