Tom is on the right path. It sounds like the VITC has scrolled down a bit and onto your screen. This staggered white line is supposed to be above the video frame, but if your deck going in or capturing device are not set correctly for reference then you see the white lines.
This would explain why your video has the lines on it in quicktimes, but then when you go out to tape the deck going outward sees reference and lines up the video correctly.
Try playing with your reference or blackburst generator.
Adam Polanger
( I dont know everything, but I know people who do)