Axes3D voxels with alpha rendered wrong -- surfaces seem to cancel #9745

Bug report

Bug summary

The shading of the voxels when using alpha looks off, when they overlap, shades seem to cancel each other out.

Code for reproduction

from mpl_toolkits.mplot3d import Axes3D

test_data = np.array(
      [[[ 0.005,  0.005],
        [ 0.000,  0.035]],

       [[ 0.005,  0.000],
        [ 0.005,  0.010]]])
alphas = np.divide(test_data,np.max(test_data))/2.0

Actual outcome

Expected outcome

GIven the data source, I would have expected a result more like this, which was produced with the code found at

http://stackoverflow.com/questions/30715083/python-plotting-a-wireframe-3d-cuboid?noredirect=1&lq=1

Matplotlib version

• Operating system: Mac OS X
• Matplotlib version: 1.5.3
• Matplotlib backend (print(matplotlib.get_backend())): module://ipykernel.pylab.backend_inline
• Python version: Python 2.7.10
• Jupyter version (if applicable): 1.0.0