Does this happen with all inputs, or just the cable box?
My two week old Samsung LE40A856S1MXXU has displayed some odd behaviour whilst watching ITV HD from a Humax Foxsat-HD box (FA CUP MAN U Vs SPURS).
Around ten times during the game the screen either faded to full white or changed to vertical stripes, this was only cured with a TV power cycle. The Freesat box is connected via the HDMI1 port on the TV.
Any ideas on correcting this fault through settings or if the set needs to be returned?