The character I'm referring to is a harsh, vegetal bitterness more than astringency. It may be that Polyclar helps diminish this (I haven't done a side-by-side to compare relative amounts of this character), but it certainly doesn't eliminate it in my experience.
The fine hop particle idea jives with my experience that whole cone hops don't cause this issue. My only issue with this is that in my experience this harsh bitterness never fully goes away. You would think that particles in suspension would drop out completely if given enough time.
This is something I have run into in the past with keg hopping - not so much medicinal astringency per se as noticing very fine hop particles that made their way through a strainer bag, giving the beer the vegetal, harsh character you mention. I don't blame the strainer bag solely, more the bag sinking down near the dip tube and the suction created through the dip tube pulling those particles from the bag.
The solution for keg hoppers IMO is using the Clear Beer Draft System, which allows you to pull the dip tube, weight the hop bag to the bottom, and draw beer from the top of the keg well away from the bag. Not to mention the beer at the top of the keg is always clearer than the beer on the bottom (barring hazy or deliberately hazed styles). Regardless, I'm noticing a huge dropoff in harsh particulate and getting clearer beer quicker, with no more gelatin.
Combining this draft system with keg hops (on the bottom) and spunding to purge the keg completely during the dry hop period has solved the dry hopping conundrum for me. $0.02 .http://www.clearbeerdraughtsystem.com/