Hmmm... perldoc.perl.org doesn't have 5.14 as an option yet. I assume that the 'r' option is meant to prevent things like this:

  my @list = (... stuff ...);
  my @other_list = map { s/SOMETHING//; $_ } @list;

(The result of this is that @other_list and @list are equal because the substitution destructively affects the original list.)