If it only occurs on scene changes I guess is IVTC failing, try using Decomb for IVTC instead of DVD2AVI's "Force Film", it solved this problems for me. I mean, set Field Operations to None in DVD2AVI when you save the project, and when you select Save & Encode from the file menu in the preview window, enable "Inverse Telecine" under "Field Operations". This happen sometimes, because DVD2AVI's inverse telecine is not as good as in the Decomb filter used by Gordian Knot.