Periodic BDM segfault in 1.2.0

Using 1.2.0 stable, built with dorsal. I get either a segfault (or occasionally a hang) with the code below.

Code:
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from dolfin import *

def SinglyPeriodicBC():
    class PeriodicBoundaryX(SubDomain):
        def inside(self, x, on_boundary):
            return on_boundary and near(x[0], 0)
        def map(self, x, y):
            y[0] = x[0] - 1
            y[1] = x[1]

    pbc = PeriodicBoundaryX()
    return pbc

mesh = UnitSquareMesh(16, 16)
pbc = SinglyPeriodicBC()
print "1"
T1 = FunctionSpace(mesh, 'CG', 1) # works
print "2"
T2 = FunctionSpace(mesh, 'CG', 1, constrained_domain=pbc) # works
print "3"
S1 = FunctionSpace(mesh, 'BDM', 1) # works
print "4"
S2 = FunctionSpace(mesh, 'BDM', 1, constrained_domain=pbc) # fails
print "5"
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Output:
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atm112@ae-amcrae:~/Dropbox/FEniCS/scratch$ python BDMbroken.py
1
2
3
4
[ae-amcrae:07493] *** Process received signal ***
[ae-amcrae:07493] Signal: Segmentation fault (11)
[ae-amcrae:07493] Signal code: Address not mapped (1)
[ae-amcrae:07493] Failing at address: 0x3adca38
[ae-amcrae:07493] [ 0] /lib/x86_64-linux-gnu/libpthread.so.0(+0xfcb0) [0x7f885bc23cb0]
[ae-amcrae:07493] [ 1] /home/atm112/local/fenics/lib/libdolfin.so.1.2(_ZN6dolfin13DofMapBuilder32build_constrained_vertex_indicesERKNS_4MeshERKSt3mapIjSt4pairIjjESt4lessIjESaIS5_IKjS6_EEERSt6vectorImSaImEE+0x3a9) [0x7f88552ddcf9]
[ae-amcrae:07493] [ 2] /home/atm112/local/fenics/lib/libdolfin.so.1.2(_ZN6dolfin13DofMapBuilder9build_ufcERNS_6DofMapERSt3mapIiiSt4lessIiESaISt4pairIKiiEEERKNS_4MeshEN5boost10shared_ptrIKS3_IjS3_IjS6_IjjES4_IjESaIS6_IKjSH_EEESI_SaIS6_ISJ_SM_EEEEENSG_IKNS_11RestrictionEEE+0x276) [0x7f88552df1e6]
[ae-amcrae:07493] [ 3] /home/atm112/local/fenics/lib/libdolfin.so.1.2(_ZN6dolfin13DofMapBuilder5buildERNS_6DofMapERKNS_4MeshEN5boost10shared_ptrIKSt3mapIjS8_IjSt4pairIjjESt4lessIjESaIS9_IKjSA_EEESC_SaIS9_ISD_SG_EEEEENS7_IKNS_11RestrictionEEE+0xdc) [0x7f88552e3b4c]
[ae-amcrae:07493] [ 4] /home/atm112/local/fenics/lib/libdolfin.so.1.2(_ZN6dolfin6DofMapC2EN5boost10shared_ptrIKN3ufc6dofmapEEERKNS_4MeshENS2_IKNS_9SubDomainEEE+0x6b9) [0x7f88552f2279]
[ae-amcrae:07493] [ 5] /home/atm112/local/fenics/lib/python2.7/site-packages/dolfin/cpp/_fem.so(+0x85d03) [0x7f883b46fd03]
[ae-amcrae:07493] [ 6] python(PyEval_EvalFrameEx+0x48d8) [0x49c4d8]
[ae-amcrae:07493] [ 7] python(PyEval_EvalCodeEx+0x1a0) [0x49f1c0]
[ae-amcrae:07493] [ 8] python() [0x4a8960]
[ae-amcrae:07493] [ 9] python(PyObject_Call+0x36) [0x4e9f36]
[ae-amcrae:07493] [10] python() [0x4ec11a]
[ae-amcrae:07493] [11] python(PyObject_Call+0x36) [0x4e9f36]
[ae-amcrae:07493] [12] python() [0x4eb39e]
[ae-amcrae:07493] [13] python() [0x4db6a6]
[ae-amcrae:07493] [14] python(PyObject_Call+0x36) [0x4e9f36]
[ae-amcrae:07493] [15] python(PyEval_EvalFrameEx+0x86a) [0x49846a]
[ae-amcrae:07493] [16] python(PyEval_EvalCodeEx+0x1a0) [0x49f1c0]
[ae-amcrae:07493] [17] python() [0x4a8960]
[ae-amcrae:07493] [18] python(PyObject_Call+0x36) [0x4e9f36]
[ae-amcrae:07493] [19] python() [0x4ec11a]
[ae-amcrae:07493] [20] python(PyObject_Call+0x36) [0x4e9f36]
[ae-amcrae:07493] [21] python(PyEval_EvalFrameEx+0x86a) [0x49846a]
[ae-amcrae:07493] [22] python(PyEval_EvalCodeEx+0x1a0) [0x49f1c0]
[ae-amcrae:07493] [23] python() [0x4a8a92]
[ae-amcrae:07493] [24] python(PyObject_Call+0x36) [0x4e9f36]
[ae-amcrae:07493] [25] python() [0x4ec11a]
[ae-amcrae:07493] [26] python(PyObject_Call+0x36) [0x4e9f36]
[ae-amcrae:07493] [27] python() [0x4eb39e]
[ae-amcrae:07493] [28] python() [0x4db6a6]
[ae-amcrae:07493] [29] python(PyObject_Call+0x36) [0x4e9f36]
[ae-amcrae:07493] *** End of error message ***
Segmentation fault (core dumped)
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