Gotta love that analogue goodness.
As far as your trouble is concerned, I have no clue. It could be due to the fact that the program is not getting the right fields into their correct frames.
Edit: Crap, I should read posts more carefully before I reply. Sorry for the redundant/useless answer. I'm actually clueless as to why this is happening. I'm not very experienced.
maybe this'll help: http://www.doom9.org/ivtc-tut.htm