I have a model inceptionfeaturesmodel, that takes a (batch_size , 3, 299, 299) input image_variable and computes (batch_size , 35, 35) output names prediction.  When I do prediction[0][0][0].backward() and check image_variable.grad, ideally grad of all inputs except first image should be zero(because they are not used in computing output of the first image. ). But they are not. Any idea why?