Solved by tristanz in post #2 
              
              
                I found an explanation here: https://github.com/pytorch/pytorch/issues/1820#issuecomment-309188062. 
“The (unusual) format of a PackedSequence object is the way it is because of the API of cuDNN’s RNN/LSTM functions, which expect a time-sequence of variable-length batches rather than a batch-sequenc…