Function.split() does not properly handle constrained domains

[Tormod Landet]

Using this code on FEniCS 1.5 prints "4, 5, 5". The expected output is "4, 4, 4"

from dolfin import *

mesh = UnitIntervalMesh(4)

class PeriodicDomain(SubDomain):
    def inside(self, x, on_boundary):
        return near(x[0], 0)

    def map(self, x, y):
        y[0] = x[0] - 1.0
cd = PeriodicDomain()

V = FunctionSpace(mesh, 'CG', 1, constrained_domain=cd)
Vmix = V*V

u = Function(V)
umix = Function(Vmix)

umix1, umix2 = umix.split(True)
print len(u.vector()), len(umix1.vector()), len(umix2.vector())

Using a FunctionAssigner seems to work properly, at least this prints "4":

Vmix0 = FunctionAssigner(V, Vmix.sub(0))
Vmix0.assign(u, umix.sub(0))
print len(u.vector())

[Tormod Landet]

Duplicate of #405.