http://scotgoespop.blogspot.co.uk/2014/07/are-peter-kellner-and-yougov-yes.html
The "Kellner Correction" mentioned in this article was removed from their methodology in August, explaining in part why their last two polls have shown a seemingly large rise for yes. Basically, their pre-August method differed from standard polling practice so was deemed to be unreliable, so they changed it back to a more standard method.