I had a very similar situation this summer. Brewed a 10 gallon batch of a Pale Ale which I brewed twice before, and wanted to load up the finishing hops instead of dry-hoping. I let it stand for 15 minutes after flame-out, before cooling & whirlpooling.
1 oz Columbus (60 min)
1.5 oz Amarillo (20 min)
2 oz Cascade (8 min)
2 oz Casacde (2 min)
2 oz Cascade (0 min)
2 oz Nugget (0 min)
All the cascade & nugget where homegrown hops from 2011, and vacuum packed.
The 1st time I used this recipe, it had dry-hops as well. All hops 2011 batch. It was a really nice beer. No defects.
The 2nd time, I used a 2010 bag for the dry-hops, and had a badly grassy beer. Barely drinkable. I also had some other brewday issues, which contributed to a bad beer. So I suspected that older bag of homegrown hops might have been bad...
This last time, I used all 2011 hops and got rid of the dry-hop. I also let the 0-min addition steep for 15 mins, before whirlpool & cooling. This batch was more drinkable, but again with the grassy flavors.
I know that improperly dried or young homegrown hops can cause grassy flavors, but that 1st batch came out so well! However, I also read somewhere that there is such a thing as 'too many' late-boil hops... ?..
I'm not sure what caused it, but thouht I'd share and let you know, you're not alone.
Would also like to hear others thoughts on it...