reconfigure --unstacked doesn't quite work for lp branches

I pushed up a test branch which is unrelated to trunk

$ bzr push
Using saved push location: lp:~thumper/wikkid/sandbox
Using default stacking branch /~wikkid/wikkid/trunk at lp-66503888:///~thumper/wikkid
Created new stacked branch referring to /~wikkid/wikkid/trunk.
HPSS calls: 21 (0 vfs) SmartSSHClientMedium(bzr+ssh://<email address hidden>/)

Now I tried to unstack it:

tim@elwood:~/src/wikkid/sandbox$ bzr reconfigure --unstacked lp:~thumper/wikkid/sandbox
bzr+ssh://bazaar.launchpad.net/~thumper/wikkid/sandbox/ is now not stacked

bzr: ERROR: Lock not held: RemoteRepository(bzr+ssh://bazaar.launchpad.net/~thumper/wikkid/sandbox/.bzr/)
HPSS calls: 22 (9 vfs) SmartSSHClientMedium(bzr+ssh://<email address hidden>/)
HPSS calls: 11 (6 vfs) SmartSSHClientMedium(bzr+ssh://<email address hidden>/)

It's straightforward to reproduce. The traceback in ~/.bzr.log looks like:

Traceback (most recent call last):
  File "/home/andrew/code/bzr/bzrlib/commands.py", line 878, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/home/andrew/code/bzr/bzrlib/commands.py", line 1082, in run_bzr
    ret = run(*run_argv)
  File "/home/andrew/code/bzr/bzrlib/commands.py", line 686, in run_argv_aliases
    return self.run_direct(**all_cmd_args)
  File "/home/andrew/code/bzr/bzrlib/commands.py", line 690, in run_direct
    return self._operation.run_simple(*args, **kwargs)
  File "/home/andrew/code/bzr/bzrlib/cleanup.py", line 122, in run_simple
    self.cleanups, self.func, *args, **kwargs)
  File "/home/andrew/code/bzr/bzrlib/cleanup.py", line 156, in _do_with_cleanups
    result = func(*args, **kwargs)
  File "/home/andrew/code/bzr/bzrlib/builtins.py", line 5462, in run
    reconfigure.ReconfigureUnstacked().apply(directory)
  File "/home/andrew/code/bzr/bzrlib/reconfigure.py", line 70, in apply
    branch.unlock()
  File "/home/andrew/code/bzr/bzrlib/decorators.py", line 222, in wrapped
    return unbound(*args, **kwargs)
  File "/home/andrew/code/bzr/bzrlib/remote.py", line 2476, in unlock
    self.repository.unlock()
  File "/home/andrew/code/bzr/bzrlib/decorators.py", line 222, in wrapped
    return unbound(*args, **kwargs)
  File "/home/andrew/code/bzr/bzrlib/remote.py", line 1119, in unlock
    return lock.cant_unlock_not_held(self)
  File "/home/andrew/code/bzr/bzrlib/lock.py", line 105, in cant_unlock_not_held
    raise errors.LockNotHeld(locked_object)
LockNotHeld: Lock not held: RemoteRepository(bzr+ssh://bazaar.launchpad.net/~spiv/wikkid/testonly/.bzr/)