Not sure if the 'ingredients\recipes' forum is the right one to post to but since I don't think this is from a flaw in brewing but rather a specific hop variety I thought it might be the correct venue.
Anyway, every now and then I'll be drinking an IPA and get a slight soapy flavor out of it. I get this occasionally from my own IPAs too. I've seen this descriptor on beeradvocate in reviews of certain brews, so I know its not just me.
I don't think we're talking about the break down of fatty acids (sitting on trub too long at high temps.) I think its more a certain hop or something.
I get it occasionally from SN Torpedo (both clone and commercial) but only very, very vaguely and not always. It's a subtle thing and hard to describe but it really is a slight soap taste. I never get this from non-IPA brews so that's why I think its a hop. Maybe one of the modern american hops (citra, simcoe or amarillo)? Those seem to be in all the brews I pick this up in.