Avoid the Quicktime H264 codec (you are using it when you export straight from Avid [QT export module] or when exporting from QT Pro).
The issue of the gamma shift has something to do with Apple’s H264 QT codec. Google ‘gamma shift h264’ and you will see many more people experiencing the issue.
Try to use something like the Main Concept x264 encoder that is in Sorensen Squeeze, for example (QT ref or QT Same-As-Source from Avid, convert to 264 using Squeeze).