TW-1420, TW-1421, TW-1422

- TW-1420 Modifying 'uuid' fails to generate error (thanks to Black Ops Testing).
- TW-1421 Modifying 'uuid' with bogus value can corrupt undo.data (thanks to
          Black Ops Testing).
- TW-1422 Attempt to modify 'id' attribute creates an id attribute (thanks to
          Black Ops Testing).