I've just, again, reproduced the black screen on ITV2...
Settings are default from Factory Reset, except set to 1080P and Digital Sound to Stereo.
Watching live TV on ITV2. Into Recordings, select a recording and either Resume or Watch From Start. Watch recording for around 30 secs then repeatedly press BACK to return to live TV. As soon as you leave the actual recording and into the Recordings display the PIP is black and this persists when you return to live TV. In live TV with black screen, no audio, press EXIT and picture returns. Equally when using EXIT to return from the recording to live TV the problem does not occur. Not on all channels but when it does occur on a channel it is constantly repeatable.
EDIT: I've played around with a variety of picture/sound settings but the problem seems to be independent of these. Put together with my earlier report of the picture display frequently spilling over the edge of the TV screen, so for example the bottom of the EPG disappears, then this could maybe be an HDMI change.