@tendonut yeah does seem reminiscent
Roku Ultra received in the mail today.
Firmware: 8.0.1 (updated as soon as it connected to the internet)
At first I was surprised that my TV 'format' menu would go haywire when the flickering happened as well, but now that I'm thinking about it, it makes sense. Input being temporarily interrupted would do that. Restarting, switching resolution between 720 & 1080, nothing seems to help. I've unchecked the "Control Other Devices" checkbox (which I had high hopes for!) but that didn't help either.
So my problem could very well by my ancient TV (been rocking this thing since 2007!!) that only supports 1080i/720p or possibly the questionable HDMI cables I've tried. However the fact that so many other people are having this issue makes me think I should just return it