Yeah, does seem like that. Trying to redefine $ssh inside the thread yeilds:

Attempt to free non-existent shared string 'GEN0', Perl interpreter: 0
+x8990e48 at Configuration.pl line 41, <> line 3.
Segmentation fault
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If I try to completely make up a whole new connection like so:

        async {
            my $ssh2 = Net::SSH2->new();
            $ssh2->connect($host);
            $ssh2->auth_password($user,$password);
            print "Upgrading firmware, this will take about 3 minutes.
+\n";
            my $chan2 = $ssh2->channel();
            $chan2->exec("/sbin/fwupdate -m\n");
            $chan2->close;
        }->detach;
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I get this error:

Attempt to free non-existent shared string 'GEN0', Perl interpreter: 0
+x83f4e98, <> line 3.
Unbalanced string table refcount: (1) for "GEN0" during global destruc
+tion.
Unbalanced string table refcount: (1) for "/usr/share/perl/5.12/Symbol
+.pm" during global destruction.
Scalars leaked: -6
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This error is not fatal though but it apparently does not pass beyond this and my script hangs.