[mabrungard]

Careful, tannins are only one form of polyphenol.

From Wikipedia: Polyphenols are generally divided into hydrolyzable tannins (gallic acid esters of glucose and other sugars) and phenylpropanoids, such as lignins, flavonoids, and condensed tannins.

[richardt]

I just got done with an IPA brewed with Wyeast 1056.  I noted the same phenomenon that you've described--especially when taking hydrometer readings at fermentation temps (64-68 F) and tasting the beer sample afterwards.  Chilling the finished beer to 33-34F for several days brighted up the beer considerably and got a lot of the bitterness to go away (adsorbed onto the yeast).  Now it tastes like an IPA should.  Bitter, but not unpleasantly so.

IMO, 1056 can be a little powdery sometimes.  It seemed to flocculate well with the first generation IPA I brewed, but, now that we're on the 4th generation (4th batch of beer), I think it's time to get some fresh yeast from the source.  

Regardless, the beer tastes good now that the yeast have dropped out and the bright beer is in kegs.  5 gallons disappeared in two nights during the Thanksgiving weekend (family, friends, parties).