The definition of “same” padding only gives the same output size when stride = 1. If stride > 1, then the size will be smaller even with “same” padding. Here’s a thread which discusses that in more detail. Actually this thread is much more detailed and shows actual results, although it only covers Conv2D, not pooling. In the Conv2D case it is definitely not true that “same” padding is a NOP when stride > 1. It’s just that it does not give the same output size in that case. We need to run the same experiment with pooling, though.