You shouldn't load it via ffdshow. The problem is that DV-YV12 and MPEG2-YV12 is sampled differently. This implies that the conversions DV-YV12 -> YUY2 and MPEG2-YV12 -> YUY2 (the latter is what avs does) should be done differently.
I will add 'DV-YV12 -> YUY2' one day to my filter, but don't have time now.
Bottom line, load your dv with avisource