Before revision:  However, it is often overlooked that the decoder obtains only a single view of the source sequences, i.e., the representations generated by the last encoder layer . Although those representations are supposed to be a comprehensive, global view of source sequences, such practice keeps the decoders from concrete, fine-grained source information generated by other encoder layers .
After revision:  However, it is often overlooked that the decoder obtains only a single view of the source sequences, which might lead to insufficient training of the encoder layer stack due to the hierarchy bypassing problem .