Your broker knows when you're doing that. Don't forget that they have a history of your trading patterns. And if your broker just happens to be the MM (TD, in this case), they can make you pay more for your new shares, killing that little profit that you just made and turning it into a little loss. Yes, that happened to me back in October and I learned the lesson. The greedier you get, the more chance for failure.
So I've worked around it, by holding and keeping my averaging down, to smaller amounts of shares. Better chance of success that way, IMO. Remember that the shorters, hedgers, etc., believe that this is their money to make, not yours.
Be careful, don't get too greedy and do your DD.
strato