This probably isn't the single solution to the problem, but it sounds like one thing you ought to do is use a protein filler on the ends when you dye those sections. That always helps even things out when I color. When you had those sections just bleached (not yet colored), was there a lot of difference in color at that point? If the roots were orange and faded to yellow and white, that might be why you had a gradient going on there. Your stylist is right, double bleaching is sometimes a good idea when you have layers of color in your hair beforehand..