Comment # 8 on bug 953051 from Josef Reidinger

So in the end I cannot reproduce it. Only thing that comes to my mind is
non-standard characters in password or different shell.
Christian - does your pwd contain special characters? ( if you can reproduce it
with trivial pwd like test it helps to indicate possible location ) and also
what shell do you use?

can you also try to run on CLI ( explicit enter is important )

echo 'test
test' | LANG=C grub2-mkpasswd-pbkdf2