Why are the seeds different when going from seed to mnemonic and back using bx? From an example in the documentation:

$ bx seed | bx mnemonic-new | bx mnemonic-to-seed | bx hd-new


655a1ed2d4fef69bb314198c7327f23c
grab special regret prepare urge evidence slush lobster midnight odor wish ketchup
57bae342ae8e69eb63f17ef993a90a59159e0f78114b602bf0ebabfec0e5d086e883c31975bf03f8a47a32853452623094d1303fd0549745db457145e5756582
xprv9s21ZrQH143K43CUCgNp5SmXzg2axQx2P4WupA2zEnKpFM19QfqfdqfpJR3yfzAXZnsHeUaQhWQMwyuqL8DbdeLeCbdMoKNn6pCY4RUn2pK

In Mastering Bitcoin, the example given here shows it going back to the seed that was originally created; this was done using an older version of bx though. Can someone explain how the seeds from line 1 and line 3 in the example are encoded/related?
They adopted bip39 where the seed mnemonic is run through a key derivation function to derive the seed. This is an irreversible step.