How can we force someone to leave chips in the pot when it was obvious that he didn't understand the bet in front of him? There are exceptions to almost every rule, and I think as long as the bet was retracted before the next player reacts, then I think the correct call is to let the player take their bet back. Of course if the next player takes any action, then it's too late. I think that is one of the reasons why the substantial action rule was created. To protect a player from an unclear bet. What would you do, if Player A bet 200 and Player B pushed out 1200 and Player C said raise and pushed 400 into the pot? You would have to assume that Player C was unaware of the raise, right?
Players have a responsibility to pay attention to the action, but I think that the dealer is just as responsible to control the action. In my opinion, an honest mistake should be handled with a warning. If the same player repeats the infraction again, that is a different story. Repeat offenders, or those acting with intent should be forced to leave their bet in the pot, or call, as pineforest suggested.
That's the way I see it.