the videoclips I use were created through Openshot (from a MTS video of my camera) with the profile:
Vimeo HD --> 720p 25 frames --> high quality (I think it generates mp4 x264 files?)
I have this problem in a very intense way when I use any one of these videoclips and try to generate a new video clip by going to the "speed" tab and make the video play backwards (reverse).
Then at the beginning of the new exported video I get black and white frames.
So it is from Vimeo HD to Vimeo HD export.