Photoshop :: Momentary Gamma Shifts In CS6 Composed Image H.264 Video

Having discovered the problem in a more complex scenario, I've narrowed down to a simple set of jpg images placed sequentially in a video group, and exported as an h.264 video from Photoshop PS6. All is on Windows 7 Professional SP1, all software involved completely up-to-date.
 
I first noticed the gamma shift using the 'High Quality' preset. It occurs with variations on Vimeo 29.97 and Youtube 29.97 presets. The gamma problem does not occur on HD 720p or 1080p 29.97 presets.
 
When I view the resulting video through Quicktime, I see a gamma shift for a moment on the first image, making it look washed out. After another moment, the gamma goes back to normal. On other players such as Windows Media or VLC, no such shift is visible.
 
Interestingly, the shift comes at 1 second when exporting to the Vimeo 29.97 preset, or 'High Quality', while at 3 seconds on Youtube 29.97. Similarly, the shift back occurs at 2 seconds, or 6 seconds for Youtube.
 
What the gamma shift looks like sounds like the now age-old Apple Quicktime fault on h.264. -- except it occurs only for one or a few seconds, then reverts to proper gamma, instead of continuing..
 
With the simple setup of single image (jpg) sequence, it occurs only on the first image. With a more complex scenario, some actual videos included, I've seen it occur on every jpg -- or on some -- in a sequence.
 
This is very repeatable here - 100%.