jamesp2,
That's rather elemental, my dear Watson ... any change in ISO from a "native" sensor point in nearly any cam may get less-than-optimal DR, noise, color-clarity, and a host of other things. BlackMagic cameras are no different in this ... it's in the beast of digital sensors & "processing engines". Each one will have its own trigger points for losses of X type, but they all do. And still, one does choose to accept the added noise & drop of DR to shoot at ISO 1600 if it means the dif between getting something & getting nothing.