Yeah mine goes from 20:1 to LEAN to AIR on my PLX when i down shift off long freeway off ramps. Fuel just cuts off. I know i was surprised too.
Also for WOT tuning my wideband is still stand alone so what i have done is have someone with me watch the wideband display while i hammer it. Then they tell me what were the numbers that they saw. I compare that to my commanded(Lambse) and make changes i as i go. 13:1ish seems to be the most common targeted N/A ratio.