As everyone said, GLOB aren't lexical.

In your code, you make tied(%b), where %b isn't %main::b, it's my (%b).

So, to fix your code, just change:

  ## From:
  my(%a, %b);

  ## To:
  my %a ;
  use vars qw(%b) ;
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And now you can see the output:

tied a
tied b
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If you want to work with the reference to the tied HASH, use:

  my $b = \%a;
  tied(%$b) ;
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Or use Lexical::Alias, as japhy said. :-P

Graciliano M. P.
"The creativity is the expression of the liberty".