After a tip from a homebrewer friend via e-mail, I saw that I was getting husk in the test sample. Got a clean sample, and voila! Conversion. Strangely enough, I still hit all my numbers except the FG, which was 6 points high. PBG and OG were on the money.
Thanks for the replies, though! I usually forget the iodine, and it always works out either way. So I guess I'll forget it altogether.
It seemed like a good idea at the time...