Yes, I did.
Turns out that my DSLR was putting out signals through the HDMI connector in 2 different resolutions. One was 1080i 60, while the menus came out as 720p 60.
I spent 30 minutes on the telephone with BlackMagic tech support, then another 12 minutes working out the settings.
Sure wish these things came with decent manuals.
Thanks for your help.