No worries, INS pretty much works like this, there is no logic or sense in what they do. Hopefully you will be receiving your FP notice soon. Keep checking the case status to make sure that it is not a case of the mail getting lost. But other than that, when your case is picked up for adjudication you will be sent a FP notice. It is just that your wife got lucky. But as they are pulling up her case, yours will also get tagged since it is a primary/derivative case.