Fusel alcohol development after dry hop?

I brewed a PM version of BM's Centennial Blonde, and pitched Nottingham @ 64-65. It sat for 3 weeks in primary and it tasted great, I sampled it a few times. After the 3 weeks i dry hopped with 1/2oz of cascade pellet right into primary. 2 days later i pulled out the bucket along with 2 others for a friend to taste test. Upon removing the lid i could tell something was wrong, the smell was harsh, like grain alcohol/acetone and had the same taste. FG did not move was at stable 1.011 just like after the first week. Oddly though there was a clear layer of liquid about a 1/4" thick (presumably alcohol) on top of the beer, some of the hops were still in suspension so it was quite easy to see them floating below this layer. I'm at a loss at what could cause this, Fusel would have most likely formed during the initial fermentation and i don't think it would of gone undetected for weeks. Has anyone seen anything like this? Thanks

My problem on dry hopped ales has been phenols. I'm still trying to solve the problem. Dang chemical compounds anyway!