FCEUX Screenshot. Nestopia and Nintendulator look about the same.
Look at the bottom scanline of the first box, they did a scroll write in the middle of the frame, so half of the box is aligned to the left, but the other half is further to the right, since only the fine scroll got changed, the rest of the scroll write takes effect at the next scanline.
Also, Spartan X 2 uses CPU cycle counting for its IRQs, so it's not compatible with PAL systems without scroll splits being at different timings. (should work fine on Dendy though)