I wonder if it is an interaction between a particular recipe and Whirlfloc. The reason I say this is I do not recall experiencing this until my most recent brew - and I always use whirlfloc. It should be said that I have only done 9-10 brews since starting last Fall. The recent brew where it showed up was a Zombie Dust clone.
The unique features for this brew were: lots of Citra hops (10 oz.), and Cara-Pils grain. Honestly it looked to me like hop sludge. I always use a hop-sack, which retains most of the hop material. But maybe Citra hops have a higher percentage of really small particles that excape the hop-sack?
What do you more experienced brewers think of this idea? Is it possible that the massive fluffy trub is due to a particular recipe ingredient?
The beer in the picture above was dry hopped at a fairly typical APA/IPA rate (0.5 oz/gallon), with pellets thrown in loose. If whirlfloc tends to form a less dense trub to begin with, it is feasible that the added hop material (combined with the highly flocculant yeast) add up to really fluff up the trub.