It is if you want the 3850 to work properly. There have been a few threads on here about this same problem and the solution was to remove the older card, and if needed for more than two monitors to get another of with a different make (Nvidia for example) or a newer card of the same make that uses the same generation of driver.
Have seen threads where some have tried it with a Nvidia card from the 8xxx series and up, with a card from an earlier generation and the same thing happens. Now if the second card was a non WDDM 1.1 Nvidia card in your case, the problem wouldn't occur (two totally different drivers, not just different driver models).