There's only sence to your class bless for other classes (when you get $class as an object), if this other class can inherit over your class. So, if you get an object blessed into the main package, like your example, your package shouldn't create a object for it.

I think that to keep OO ok you should declare new() as:

sub new {
  my $class = ( @_ ?
                    ( ref($_[0]) ?
                                  ( UNIVERSAL::isa($_[0] , __PACKAGE__
+) ? ref(shift(@_)) : __PACKAGE__ )
                                  :
                                  ( $_[0] =~ /^\w+(?:::\w+)*$/ ? shift
+(@_) : __PACKAGE__ )
                    )
                    :
                    __PACKAGE__
              ) ;
  
  my $this = bless {}, $class ;
  
  ## initialyze code...
  
  return $this ;
}
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I know that is not a beautiful code, but to do what you want is that.