B is a difficult key for fiddlers--I have heard others mention it--I don't imagine that it was a difficult challenge for Dan to understand what was going on theoretically--I think that it has to do with the problems related to the fact that when you move to the dominant chord in B, you are playing in F#, which, on an untempered instrument (as the violin is) is a really problematic pitch--owing to the comma--and building a dominant scale on it is, most likely, an iffy proposition at best--