I’ve had this same problem and so far nobody has an answer. Check and see if it is “adding” a frame at your dissolves. That’s what it looks like to me when I step through frame by frame. Also, it looks fine when it is not rendered (green bar) but does the extra frame thing when you fully rneder. It’s terrible and I wish somebody out there could figure it out. I’m seeing this come up more and more.
My footage was 720p24pN P2 from an HVX-200. OSX 10.3.9, FCP 5.0.4. Same easy preset you used.