strangely I've never noticed this before, but it would seem as though you're not alone having opened ETX this morning. Have you tried asking any of the brokers? I'm aware of the pre-market "auction" but that shouldn't explain a 1 minute delay
This seems to be for the sake of the client as there can be very wide spreads for the first few minute's trading with the risk of being stopped. This happened to me on the first trading day of 2012, I had two shorts on MRW with stop at 339. After the auction the price opened at 330 and started trading at 331 but in the intervening instant the price had spiked to 340 stopping me out.
This was with IG who do open as soon as prices come through from LSE.