I wish it were so simple, but I don't think so. In fact, my main program and module both had use strict; and use warnings; originally, as I use them habitually. So much so that initially I had thought the warnings were produced because of them and reported a bug on Config::Std that it was incompatible with use warnings;. It was only later that I realized the warning didn't go away when I removed use strict; and use warnings; from my own code.

None the less, to test your assertion, I changed the main program to:

#!/usr/bin/perl
use strict;
use warnings;

use MyClass;

my $obj = MyClass->new();
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but still the warning was produced.

Then I changed the module to:

package MyClass;
use strict;
use warnings;

use Class::Std;

my $hash_ref = {};
bless $hash_ref, 'MyClass';

sub DEMOLISHx {
    print "demolishing...\n";
}
1;
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And still the warning was produced.

So, after all, the warning wasn't produced because Class::Std uses strict and warnings and my module doesn't.

Other ideas?