I am new to developing and scanning and need some scanning advice. I use an Epson V750 with Silverfast AI. To date have developed about 10 B+W (Delta 400, HP5, XP2) and 10 color rolls (Superia 400, Ektar 100, Portra 800). I am learning and refining my process with each roll and have been pretty satisfied with my results. However, I notice that after I do a prescan, the color and brightness of all frames change depending on which frame the selection marquee is covering. This is especially noticeable with a mixture of day and night shots. A frame that I am particularly happy with may change as soon as I drag the selection marquee over it i.e. the brightness increases with especially washed out highlights. Is this normal and is there anything I can do to prevent this from happening?