I have the same TV with the flashing black screen on HD broadcasts from CH4 HD, BBC1 HD and ITV HD. I have added an attenuator to reduce the digital signal strength but this has not helped the issue. It is fine on non HD content freeview but on all the HD channels you get the blacking out of picture for probably half a second, the period between flashes is very random and can be every 10 seconds to 3 or 4 minutes between flashing. There is no correlation and it is really upsetting for a new HDTV to have these issues. I have contacted the sellers but they cant add any advice.I live within 5 miles of the TV transmitter and have hence added the attenuator to reduce signal strength to 95%.
I have just purchased a Samsung UE32D5520 LED TV in the UK. It's a great picture, and the iPlayer works well.