I am maintaining a system which accepts pre-encrypted passwords from various sources. Recently I've been asked to support a system that generates hashed password like the following:

$1$ZD1qsc8PwUXqP9GihP+NHvWQ+FXap4Td0KWCMp8yrDQ=B71E718B3CC3262CC83F15B
+B2A97A2C5429B2028D217A90D6D7E275E08F68A4AE69526B8FE05CFE06EAC5B8E0958
+B372FAC6040E36BEFB0F681ADE7F7E9861BE
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which looks to me like an SHA512 hash (hex encoded) with a 32 byte salt (base64 encoded). I've tried reformatting it to crypt SHA512 standard using

use MIME::Base64 qw(encode_base64);
my $hash = "B71E718B3CC3262CC83F15BB2A97A2C5429B2028D217A90D6D7E275E08
+F68A4AE69526B8FE05CFE06EAC5B8E0958B372FAC6040E36BEFB0F681ADE7F7E9861B
+E";
my $b64hash = encode_base64(pack('H*', $hash));
my $salt = "ZD1qsc8PwUXqP9GihP+NHvWQ+FXap4Td0KWCMp8yrDQ=";
my $saved = '$6$' . $salt . '$' . $b64hash;
my $wild = "password";
print "OK" if crypt($wild, $saved) eq $saved;
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but to no avail - the salt appears to be truncated:

$6$ZD1qsc8PwUXqP9Gi$D72oiWMfTm90ZFouvu.aU3C6UCOPGKyS2jbZSKefD8IGo13x49
+7sRFX8062y30pGIIc/KtC6aq9qui.FuKm6Y1
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Then I tried Crypt::SaltedHash:

use Crypt::SaltedHash;
use MIME::Base64 qw(decode_base64);
my $password = "password";
my $crypt=Crypt::SaltedHash->new(algorithm=>'SHA-512', salt_len => 32,
+ salt => decode_base64("ZD1qsc8PwUXqP9GihP+NHvWQ+FXap4Td0KWCMp8yrDQ="
+));
$crypt->add($password);
my $shash=$crypt->generate();
my $salt=$crypt->salt_hex();
print "Salt= $salt\n"; # to show that it is using the right salt
print  "hex encoded = " . unpack('H*',substr($shash,9)) . "\n";
# the substr is required as generate prepends {SSHA512}
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but the hex encoded line doesn't match the one in the original string.

I'm wondering if the prepended $1$ is a clue? Maybe MD5 is involved somewhere along the line? Has anyone seen a hashed password like this before? And prepared to offer any hints?

Edited to include a real example