Salt string compatibility problem 4.4.10 focal

[Alex Handle]

After upgrading from Ubuntu 18.04 to 20.04 a lot of authentification problems appeared on our mail cluster (Postfix/Dovecot).

I found out it was due to the format of the salt in the hashed passphrase.
All non working hashes have a '&' character in the salt:

1$abcd&$F3E5DEjSFJpzgeU.Wzu/W.\

This salt format worked on Ubuntu 16.04 and 18.04:

perl -E 'say crypt($ARGV[0], $ARGV[1])' 'test' '$1$abcd&$F3E5DEjSFJpzgeU.Wzu/W.\'
$1$abcd&$F3E5DEjSFJpzgeU.Wzu/W.

But not on Ubuntu 20.04:

perl -E 'say crypt($ARGV[0], $ARGV[1])' 'test' '$1$abcd&$F3E5DEjSFJpzgeU.Wzu/W.\'
*0

The upstream already fixed this problem in libxcrypt 4.4.17:

"Salt string compatibility with generic implementations (issue #105)."

https://github.com/besser82/libxcrypt/blob/develop/NEWS

and here the link to the github issue and commit:

https://github.com/besser82/libxcrypt/issues/105
https://github.com/besser82/libxcrypt/commit/f05159c73a7415da1a8430ee2db6ec8035b5d2e8

It would be really nice if you could upgrade the version of libxcrypt to 4.4.17 for focal.
A package for Hirsute Hippo with 4.4.17 already exists and i installed it on one of our focal mail nodes which solved the problem, but i'm not sure if i should use libcrypt1 and libcrypt-dev dpkg from 21.04 developement version.

Thanks for your help,
Alex