Ok, take the other day for instance, I was looking through the sky interactive channels. 1 channel had rugby on it, let's say channel 1401. If I hit channel up and nothing is on 1402 and then flick back to 1401 it was ok. If I then flick up to 1402, nothing on, then 1403, nothing on, then ch- back to 1401 it is now blank. If I type in a channel number, let's say 401, it is also blank. I then had to restart the box in order to view the channels again.
It also happened if I used TS media. If I looked at something and had to search through several links to find a working one, then went back to watching tv, the channels were again blank requiring a restart. Hope this makes sense.