I re-open this issue not because it is totally, but not really functional. It does not change between every frame and I get ERR70.
Settings used: 720p 30fps audio enabled
It seems quite random which frame it over- and under-exposes. I wrote down the frames it over exposed(During this test I had the iso set to 160(like it would be without hdr), iso A to 160 and iso B to 1600). The number of the frames where: 3 11 25 33 53 67 81 94 108 115, and so on. At another clip the numbers would differ.
A strange thing I noticed was that if the "base" iso is neither iso A or B, I will actually get 3 different exposures. One will be the "base" iso, one iso A and one B. I find the base exposed frames to dominate the among the others. And maybe iso A is more common than B? Need more investigation.
The main reason why I ran into this problem was because I waned to shoot a timelapse with fps override and hdr. This is of course in 1080p with the lowest fps value selected (whatever that is exactly).