[Tanner Johnson]

I know this thread is long dead, but for all those people searching through google for the answer, this is it!

Make sure to right click on your file in the FCP Browser, go down to Item Properties, Format. From there, find Field Dominance. Right click on the options it gives you (None, Upper, Lower, Not Set) and select None.

Make sure to drag this into your timeline AND DELETE the existing footage on the timeline if you have already placed it. Render and your problem should be solved.