I'm inclined to believe that brake torque won't have any affect on a properly designed trans. Unless the clutches slip, there is no wear on the trans due to this practice.

Of course, as said above, the fluid will heat up in the torque converter as a function of time. If the brake torque is simply for three seconds or so, I don't see how any damage can occur, even if this practice is repeated on a frequent (several times per day) basis.