Problem is that Item::save_in_field modifies str_value member
 before it calls val_str but Item_copy_string::val_str just returns
this str_value as the result.
I added local String variable to the Item::save_in_field


mysql-test/r/create.result:
  appropriate test result
mysql-test/t/create.test:
  test case
sql/item.cc:
  local variable added to keep the result