I have been having the exact same problem.
My original video is a .avi, Codec H264 Mpeg-4 AVC, Planar 4:2:0 YUV, 720 x 576 pix., 25 fps, pixel ratio PAL CCIR 601, fiel dominance upper.
My FCP sequence is DV PAL, 720 x 576 pix., 25 fps, Pixel ratio CCIR (DV PAL 5:4), field dominance upper (odd).
After looking into different options I converted the original clip with Mpeg Streamclip to AppleProRes 422, Planar 4:2:2 YUV 10-bit LE, 720 x 576, 25 fps.
Also tried with a new sequence setting: AppleProRes 422, 720 x 576 pix., Pixel aspect PAL CCIR 601, field dominance Upper (odd).
I tried switching the field dominance in the sequence and when converting the video and nothing corrects the problem.
For now I’ll just add anti-aliasing filter, even if it decreases the quality somewhat.