If it was a subtitling problem rather than a faullty pixels glitch, then that would mean that it was a fault in the television software/hardware. That would be out of the BBC control.
I don't think we know where this picture has come from. It could be a problem that affected just one tv and someone took a photo of it and blogged it.
I'd like to see the whole clip before I make a judgement.
If it stayed on his face for the whole of the interview I'd be suspicious, but if it was just there for a fraction of a second, I think it's probably a technical glitch.