There appears to be a problem with shadows interfering with the object preview. Please take a look at the attached screen shot where I have recreated the problem.

I have narrowed the problem down to the Shadows Softing parameter in the Video Options. If I turn this off (i.e. set it to 0) then the problem goes away.

As you can see in the screen shot, the shadow of the mountain in the scene is corrupting the preview of the palm tree. If I move the camera around I can see the mountain's shadow move across the palm tree. You can also see smaller shadow artefacts on the palm tree's leaves (the little dark squares).