sub definitions are parsed once only. The closure retains the value it had at that point in time. Try this:

use warnings;
use 5.010;

for my $num (1 .. 5) {
    my $a = $num;

    {say "in block: $a"};

    *test = sub {
        say "in function: $a";
    };

    test()
}

__END__
c:\test>junk11
in block: 1
in function: 1
in block: 2
Subroutine main::test redefined at C:\test\junk11.pl line 11.
in function: 2
in block: 3
Subroutine main::test redefined at C:\test\junk11.pl line 11.
in function: 3
in block: 4
Subroutine main::test redefined at C:\test\junk11.pl line 11.
in function: 4
in block: 5
Subroutine main::test redefined at C:\test\junk11.pl line 11.
in function: 5
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You can disable the redefinition warning.