[David Wheeler] “Also, conversion to H264 for web viewing reduces the effect. It can be seen on the camera during playback but not while recording which leads me to think that it is something to do with the AVCHD recording system.”
Do you have footage you can link to?
[David Wheeler] “It happens in progressive mode regardless of the camera settings. (I have tried them all.)”
Are you aware that there is only one true progressive mode on the C100? 24p. 24PF and 30PF are 60i with pulldown. If you’re not removing the pulldown, this may be responsible for the issue you are seeing. You might want to try doing a comprehensive test with the 24p setting if you haven’t been shooting primarily in that mode.