matrix-free PETScKrylovMatrix works in 1.0, but is broken in fenics-dev

Consider the following snippet (due to Christian Clason):

#####
from dolfin import *

mesh = UnitSquare(32, 32)
V = FunctionSpace(mesh, 'CG', 1)
bc = DirichletBC(V, Constant(0.0), lambda x, on_boundary: on_boundary)
u = TrialFunction(V); v = TestFunction(V);
A, b = assemble_system( inner(grad(u), grad(v))*dx, Constant(1.0)*v*dx, bc)

class KrylovMatrix(PETScKrylovMatrix) :
    def __init__(self) :
        PETScKrylovMatrix.__init__(self, V.dim(), V.dim())

    def mult(self, *args) :
        y = PETScVector(V.dim())
        A.mult(args[0],y)
        args[1].set_local(y.array())

y = Function(V)
solve(A,y.vector(),b)
x_petsc = PETScVector(V.dim())

KrylovSolver = PETScKrylovSolver("cg","none")
KrylovSolver.solve(KrylovMatrix(), x_petsc, down_cast(b))

print (y.vector()-x_petsc).norm("l2")
#####

This code works with Dolfin from the fenics PPA:

[pef@doodson:/tmp]$ dpkg -l python-dolfin
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Description
+++-=====================================================-=====================================================-==========================================================================================================================
ii python-dolfin 1.0.0-2~ppa1~natty1 Python interface for DOLFIN
[pef@doodson:/tmp]$ python testMatrixFreeKrylov.py
1.93697136644e-08

but fails with Dolfin from the fenics-dev PPA:

[pef@caoimhe:/tmp]$ dpkg -l python-dolfin
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Description
+++-=====================================================-=====================================================-==========================================================================================================================
ii python-dolfin 1.0.0-2+bzr6524~ppa1~maverick1 Python interface for DOLFIN
[pef@caoimhe:/tmp]$ python testMatrixFreeKrylov.py
Traceback (most recent call last):
  File "testMatrixFreeKrylov.py", line 23, in <module>
    KrylovSolver.solve(KrylovMatrix(), x_petsc, down_cast(b))
  File "testMatrixFreeKrylov.py", line 15, in mult
    A.mult(args[0],y)
TypeError: in method 'GenericMatrix_mult', argument 2 of type 'dolfin::GenericVector const &'