I'd say the carbs + fat mixing phenomenon is being taken a bit too literally. We've got people on here that are worried about 5g of carbs mixed with their flax oil when obviously 5g of even dextrose isn't enough to make a significant surge in insulin, which btw is what we're trying to avoid while having large amounts of fat being digested.
I think mixing carbs + fats in high amounts, and/or bad sources is obviously a bad idea, but don't get so wrapped up in it. So long as you aren't getting like 20g of saturated fat along with 50g of simple carbs I'd say you're probably gonna survive to tell about it. I also think that mixing macronutrients is of more importance while bulking since your body is in a constant hypocaloric state and you have more chance of storing the surplus of calories as fat. If you're cutting then you are in a caloric deficit at almost all times anyways so you shouldn't be storing any of those calories, except during post workout nutrition which we can all agree is the one time we don't want fat period.
Use common sense reasoning. Eating a large bowl of cornflakes with whole milk and a scoop of peanut butter on white toast isn't a wise choice, even if you're in a hypercaloric state. However getting 5-10g of healthy fats with your c + p meals, or 10-20g of low GI carbs with your p + f meal probably won't make a big difference while dieting and probably not even while bulking.