Default Screen Problems (Flicker)

I've searched and seen few post about this, but not much more information, I've rooted and installed cyagenmod 11, an started noticing, for example opening a folder, on the home screen, the brightness of the screen increases for a second, and then decreases, or scrolling thru instagram, or something u can notice the screen gets bright, dims a lil slightly, depending on whats being displayed on the screen, darker images, vs white backgrounds .etc, I just flashed back to stock, and notice it does the same.

I have auto brightness turned off, and brightness set around 40-60 %, is this a defect? software issues? or what.. wanna make sure before I send this back..

Thanks