Globs are not lexical (unless diotalevi is involved ;) e.g

use strict;

use Tie::Hash;

my(%a, %b);

tie %a, 'Tie::StdHash';
print( (tied(%a) ? 'tied' : 'NOT tied'), " my %a\n");

*b = \%a;

print( (tied(%main::b) ? 'tied' : 'NOT tied'), " %main::b\n");
print( (tied(%b) ? 'tied' : 'NOT tied'), " my %b\n");

__output__

tied my %a
tied %main::b
NOT tied my %b
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As you can see your problem is that you're testing the lexical %b and not the package %b.
HTH

_________
broquaint