When I make chocolate pudding on the stove, I have been getting inconsistent results. Usually, the pudding thickens, then comes to a boil, and sets perfectly. Occasionally, however, it thickens, but doesn't come to a normal boil-it seems to bubble up, almost like scalded milk, but doesn't set and is more like thick pudding soup-still edible, but not pudding-like in consistency. I can't tell what I'm doing wrong. I read somewhere that mixing too vigorously after the cornstarch begins to thicken breaks down the starch particles. Could that be it? Thanks.