Warped tangs aren't unusual. It's very easy for the tang to warp during the heat treating process and without solid quality control at the factory, they won't be culled or corrected.
And the good news is that they can be corrected most of the time with a vise or heavy duty press using two brass rods to support either side as contact points and one brass rod on the high side as a fulcrum to bend the blade straight again. This will usually leave the blade undamaged if done carefully because it's a slow pressure. Trying to hammer it straight can work sometimes and can break the blade a lot of times.