I think that this problem comes from how you used MPEG Streamclip.
Try this:
Open your clip in MPEG Strea,clip.
Go to the clip start.
Going frame by frame, find a piece of material that has movement. You will probably now better see the “comb effect” to which you refer. You might find, for instance, that there are two “combed” frames, followed by three normal frames. These combed frames are interlaced frames.
Move forward frame by frame until you get to the end of two interlaced frames and the start of the three normal frames.
Hit “i” (in point)
Now, click in the that box on the screen called “deinterlace”.
Make your movie.
If there are still interlaced frames present when you have done this, then you should try a slightly different “i” point.
This should work.
Best
Harry.