Hi,
Yes, I agree the Medea disks would be the cause of this problem. The Medea guys are working hard on this, and have been posting updates here on the Kona Cow forum, so we should all be kept up to date on this.
It might be worth using Online JPEG only on that disk until compatibility is sorted out by Medea. At the lower compressed data rates, the Medea disks seem to work ok.
Regards,
Grant Petty
Blackmagic Design
http://www.blackmagic-design.com