Brightness Shift on D800E

Hi there,

I am recording a clip of some subjects on a white background.

Camera is Nikon D800E, on tripod, static, Mode set to M, f/5.6, S 1/50, Manual autofocus, WB daylight, ISO 200. Recording is in DNxHD on Atomos Ninjia 2. Scene is illuminated with daylight fluorecent bulbs trough diffusing sheets.

Well, the problem is that depending on the number of objects on the scene the brightness of the objects is changing:

- with few objects (lots of white) the objects looks like "washed"

- adding more and more object in the scene (less white) theys colors/brightness/contrast improve significantly.

- made a test, filling the scene with many objects (no more white background) their color is matching the real thing.

Why is happening that?

What I can do to fix that?

Thanks,

Antonio