LUSolver with annotation turned off raises exception

The following code gives the exception: "Your matrix A has to have the .form attribute: was it assembled after from dolfin_adjoint import *". (The purpose of the code is to be able to turn annotate completely on and off.) Perhaps the check for the .form attribute should be when calling solve (with annotate == True) rather than in the creation of the LUSolver?

from dolfin import *
from dolfin_adjoint import *

mesh = UnitInterval(10)
V = FunctionSpace(mesh, "CG", 1)
u = TrialFunction(V)
v = TestFunction(V)
a = u*v*dx

A = assemble(a, annotate=False)

solver = LUSolver(A)