errornorm() in the tutorial won't run in parallel

The errornum(u_e, u, Ve) code in the tutorial (page 25 in the final version) won't run in parallel.

The line which is causing the problem is:
e_Ve.vector()[:] = u_e_Ve.vector().array() - u_Ve.vector().array()

Running the code with mpirun -np 2 gives:
Traceback (most recent call last):
  File "calibrate_difference.py", line 19, in <module>
Traceback (most recent call last):
    e_Ve.vector()[:] = u_e_Ve.vector().array() - u_Ve.vector().array()
  File "/usr/lib/python2.7/dist-packages/dolfin/cpp.py", line 3601, in __setslice__
    self.__setitem__(slice(i, j, 1), values)
  File "/usr/lib/python2.7/dist-packages/dolfin/cpp.py", line 3632, in __setitem__
  File "calibrate_difference.py", line 19, in <module>
    e_Ve.vector()[:] = u_e_Ve.vector().array() - u_Ve.vector().array()
    _set_vector_items_array_of_float(self, indices, values)
RuntimeError: non matching dimensions on input
  File "/usr/lib/python2.7/dist-packages/dolfin/cpp.py", line 3601, in __setslice__
    self.__setitem__(slice(i, j, 1), values)
  File "/usr/lib/python2.7/dist-packages/dolfin/cpp.py", line 3632, in __setitem__
    _set_vector_items_array_of_float(self, indices, values)

It seems the problem is caused by the numpy array. The fix is very simple. The following does exactly the same and works in parallel:
e_Ve.vector()[:] = u_e_Ve.vector() - u_Ve.vector()

The following code demonstrates this gives the right answer:

from numpy.random import rand
from dolfin import *

N = 10
mesh = UnitInterval(N)
V = FunctionSpace(mesh, "CG", 1)
u = Function(V)
v = Function(V)
w = Function(V)
z = Function(V)
q = Function(V)

u.vector()[:] = 1.0 + rand(N+1)*1e-8
v.vector()[:] = 1.0 + rand(N+1)*1e-8
w = u - v; print(assemble(w**2*dx))
#z.vector()[:] = u.vector().array() - v.vector().array(); print(assemble(z**2*dx))
q.vector()[:] = u.vector() - v.vector(); print(assemble(q**2*dx))