Interesting thread. I currently have a rye pale ale bottle conditioning. It's still not aged enough to judge it, still green, but I tried one last night and it was fairly astringent. It seemed with only upper 20s/near 30 IBUs there is no way it should have been that bitter, even if it is still green given my past brews.
My method was a partial mash. My water is quite hard, but I haven't had a problem before, but this mash was the lightest in terms of malts (3lb 6-row, 2lb flaked rye, 1/2 lb crystal 40, and 1/2 lb rice hulls, 1.25qt/lb). I'm thinking that grain bill may have been too light for my water and the mash pH was too high.
Before I jump to conclusions, I'm going to let this age for a while yet and see how it is in a few weeks/month. I might come back with a few questions about water and the Buffer 5.2.
FWIW, my water specs:
298 Hardness as CaCO3
281 Alkanity as CaCO3