I have an oatmeal stout that I mashed at 158 and used 2 lbs of oatmeal. FG=1.026. Yes I was sure it was finished, but was surprised as well. After 4 weeks of bottle conditioning I got to say, its a pretty damn good, chewy stout!
I say if it tastes good to you, forget shat the style guidelines are (unless you are trying to win a competition...)