Yes, it was to do with the HDMI CEC features. They are the things, which are suposed to auto tune say your TV to the right input, when the inputed device turns on. The NB3 hardware is suposed to support HDMI CEC.. but it seems to be flakey or send wrong signals. If you turn the HDMI CEC off on your TV, it might fix the issue.
(sometimes its called the propritary name.. vieralink, etc.. for that brand of TV)
I was experiencing the same problem with my Nextbox 3.0 having a blank screen at startup.
I read lots of posts on here and I managed to fix the problem by changing the channel at startup to "Your World This Week" (YWHD) and rebooting the box. I had made these changes the day prior, hit save and nothing happened. It was the reboot that made the changes occur.
I have a Panasonic Plasma TV and Viera Link is still active. Some other posts had mentioned turning such features "off", but in my case it didn't matter.