For whatever reason, the extra space causes different output on Windows:
$ printf '% 20d' '1' | xxd - 0000000: 2020 2020 2020 2020 2020 2020 2020 2020 0000010: 2020 2020 31 1
vs WSL:
/mnt/c/Users/Matt/hg/tests$ printf '% 20d' '1' | xxd - 00000000: 2020 2020 2020 2020 2020 2020 2020 2020 00000010: 2020 2031
Without the space, they both agree the last word is 2031. There are other
failures on Windows that I don't understand that are introduced by 46b828b85eb7
and 18415fc918a1.