I wonder if you guys aren't fermenting too warm. I know the original recipe says to ferment at 68 but everywhere else I've read about brewing with Hefe yeast says to brew much cooler than that, around 62 degrees. I know a warmer fermentation just usually means more banana flavors but maybe with this recipe for some reason a warmer fermentation is producing more off flavors than normal.
I just kegged my second batch of this beer last weekend and it came out great. I fermented at 63-64 degrees and got no off flavors, used the Wyeast strain. My first batch I followed exactly the same as this one, and got the same result. I didn't go through all the posts about people having issues but temperature control is critical (ie. fermentation chamber) with this yeast.