Error when setting colorbar in traits

Dear Mayavi developers,
I've run into (another :) ) error... This time when trying to display a colorbar within the traits example:

``` python
#!/usr/bin/env python
"""A simple example of how to use mayavi.mlab inside a traits UI dialog.

This example uses traitsUI (
`traitsUI `_ ) to create a
the simplest possible dialog: a single Mayavi scene in a window.
"""

# Authors: Prabhu Ramachandran
# Gael Varoquaux
# Copyright (c) 2007, Enthought, Inc.
# License: BSD Style.

# Standard imports.
from numpy import sqrt, sin, mgrid

# Enthought imports.
from traits.api import HasTraits, Instance
from traitsui.api import View, Item
from tvtk.pyface.scene_editor import SceneEditor

from mayavi.tools.mlab_scene_model import MlabSceneModel
from mayavi.core.ui.mayavi_scene import MayaviScene

######################################################################
class ActorViewer(HasTraits):

# The scene model.
scene = Instance(MlabSceneModel, ())

######################
# Using 'scene_class=MayaviScene' adds a Mayavi icon to the toolbar,
# to pop up a dialog editing the pipeline.
view = View(Item(name='scene',
editor=SceneEditor(scene_class=MayaviScene),
show_label=False,
resizable=True,
height=500,
width=500),
resizable=True
)

def __init__(self, **traits):
HasTraits.__init__(self, **traits)
self.generate_data()

def generate_data(self):
# Create some data
X, Y = mgrid[-2:2:100j, -2:2:100j]
R = 10*sqrt(X**2 + Y**2)
Z = sin(R)/R

self.scene.mlab.surf(X, Y, Z, colormap='gist_earth')
self.scene.mlab.colorbar()

if __name__ == '__main__':
a = ActorViewer()
a.configure_traits()
```

throws an error:

``` error
ERROR: In /Users/builder/pisi-64bit/tmp/VTK-5.6.0-3/work/VTK/Widgets/vtkAbstractWidget.cxx, line 119
vtkScalarBarWidget (0x1186380c0): The interactor must be set prior to enabling the widget
```

I'm not sure whether this is an mayavi issue or a VTK bug (or I'm missing something and this is done otherwise...).

Best regards,
Tscheik