It is based on the current view style. In your case in the image, the view style is shaded with visible edges. If you switch it to simply shaded, you will not have the edges displayed on the transparent part while using FlashFit.
I see the difference about what you say, but in ST5 it was different..not all edges were visible when you were adding a part. I'm the only in my office with this "problem" ,my colleagues still see the part as ST5 version..why??. When it's just a cilinder the problem is minimal...but when you have multiple edge of big part it's quite annoying to find the right surface! However thanks for the answer waiting for other advices!