Yup this is my #1 and perhaps only problem with this TV and one I'm hoping gets fixed by the time my return window closes. It's just not really acceptable IMO. I want to watch 3D with motion smoothing and/or w/o Cinema Smooth. Hoping this gets fixed with forthcoming firmware. I've reported the problem to Samsung etc etc.
If they fixed this I'd be happy and just enjoy the set for the foreseeable future. Because of this I'm still on the fence, even though I adore it in most respects.
Of course I still need to swap my TV because I noticed recently I too have the faint horizontal band in the upper 3D of the TV. Hoping I can get one that doesn't have the band. Checked the set on display at one of the local Magnolia stores and it too has the band.