[BScout]

Do you have any gaps/edits to the picture in the section you are bouncing? Even one frame missing in the picture or a little space before or after picture? QT doesn't mind that and fills it with filler (black or white) and it can be a flash frame or not depending on where it is (you probably wouldn't even notice if it was at the head or tail of the picture.) FCPX does not like that at all. When you render in QT, it replaces those edits with a continuous picture.