I've just picked up a new 430EX II, and have taken a few test shots. The flash is firing OK, but after setting the mode to ETTL and adjusting the flash exposure compensation to -1/3, the LCD display continues to blink. Is this normal? Also, nothing happens when I press the Zoom button on the flash. I'm using a 50D in Av mode, with a 35 f/2 lens.