always passes $str as parameter to the subroutine..

Yes - $str is the *second* argument that gets passed. The first argument will be the package name. Here's a demo:

use warnings;
use strict;
package MY_FOO;

my $str = 'this is the second argument';
MY_FOO->foo($str);


sub foo {
    print "$_\n" for @_;
}

__END__
prints:

MY_FOO
this is the second argument
[download]

(I haven't dug into your code - I'm merely guessing that this is what's happening.)

Cheers,
Rob