That's what everyone says and it doesn't happen, they just get obsessed with their 6/8 packs and don't train right or eat enough when doing their "bulk" for fear of losing it.
On the diet criticisms:
-I believe your calories are a bit low, unless your metabolism is actually that slow (and I don't think it is, or you wouldn't be 160lbs)
-Your PWO shake looks weak as hell, unless you train that lightly and without intensity
I'm no nutrition expert, only for my own diets, so I won't suggest alternatives for you. Maybe someone else will.
Lose the ab obsession, summer is almost over. At 10% BF (if that's true or accurate. At 160lb it might be, but with more mass you should be able to see your abdominals fine at 10%), if you gained some mass bulking very cleanly (ie slightly above maintenance), you will lean out faster than if you tried to cut those last 10lbs.