I think that the warping may be a product of the geometry of the chisel and how the stresses will want to pull it in different directions. Similar stresses that happen in timbers also seem to happen in steel. I have seen a 1/16 of an inch of difference at the base of a blade make the tip want to warp out more than 1/8".... stresses are neat stuff. If you want to make straightening easier, you can heat it up to 400 in the oven and then tap it while it's hot. It will be a little less likely to crack or chip.
