I’ve mixed HV20 and EX-1 footage before, but i matched up the res and frame-rates, i.e. 1080i60.
What’s your output? Try making a ProRes Timeline setting it to 1080i60 and Render your footage and export as a self-contained quicktime (Both EX-1 and HV20 Clips), bring those exported files in and try editing it on the same timeline.
hmm… I wonder what this button does…