Portions of combined movie are discolored after I join movies using QuickTime 7 Pro

I've got a bunch of .MOV files from my camera (all from the same camera with the same settings), and often I want to join 2 or more into a single video file. Using QuickTime 7 Pro, I can paste one movie onto the beginning or end of another, then File>Save As to save a combined file. However, when I do this, 4 times out of 5, the combined file gets weird during playback. The section of it that corresponds to the *first* original file is always good; however, once it moves into the second and subsequent files, it flashes colors, has discolored frames, or switches to a bizarre color scheme for a few seconds at a time.

What's the problem, and how can I combine movies without this probem and *without re-encoding*?