Adding HD movies in quicktime some go green

I've been downloading and editing mp4 youtube game walkthroughs and saving as movs (simply save- no export) These movs I've then been combining into a single larger file with the intention of playing back as a movie. However, a few copy and pastes in I discover one of the movs displays with a green overlay which can impact following added edits. Independently it plays fine and has the same properties as other files.

Any ideas as to what is causing this and how to get rid of it? I would prefer not to encode. (The mp4s use H.264 codec) also the sound files of each added movie seem to stack up rather than get added to a since track.

I've included an attachment to show the effect. I'm using Quicktime 7.6.6.