If this doesn't happen a lot then you really don't have anything to worry about, but yeah it's probably the way doing it. You have a pretty high amount taken in a small span of time. Try doing post wo shake, solid meal(chicken/oatmeal etc,), then your second shake. Should help the digestion a little bit. As for going to waste, no doubt some protein was malabsorbed, but not enough to effect you if it's not a common occurrence.