In v1.25

     static VALUE
     rb_str_clone(str)
         VALUE str;
     {
         VALUE clone = rb_str_dup(str);
         if (FL_TEST(str, STR_NO_ORIG))
>>>          RSTRING(str)->orig = RSTRING(str)->orig;  <<<<
         CLONESETUP(clone, str);
         return clone;
     }

Dave