As long as the orginal DVD does not have CSS, I use Cinematize Pro to demux – it does it in one step, I normally export to a DVCPro50 or 10-Bit Uncompressed codec, so I get 4:2:2 color space, DVCPro50 can be easier since it is 720×480 and you don’t have to deal with the 486 which 10-Bit should be.
But you switch the field dominance is why you are having problems. NEVER do that!