In what way intermittently? I have read that it is not available via the Red Button from the BBC1 HD and BBC HD channels on Freeview but only from the BBC SD channels. Or go directly to Freeview 301 for the interactive stream.
Sorry if I wasn't clear, I was referring to the news/sport/weather etc service accessed by pressing the red button (on the SD channels).
It's intermittent in that the invitation to press red is visible at the top right of the screen sometimes and not others and it will load the pages sometimes and not others. If I change to viewing via the TV pressing red works fine.
You are in the lap of the BBC for red button functionality, nothing to do with the Humax.
Edit: sorry, just read back to see that you say it works on a TV. There is nothing in the custom firmware that is likely to get in the way unless you are doing something to cause a high processor load.