TypeError: image has incorrect type (should be uint8)

Hi. I found a bug in the macos backend.

I get this error when I turn on log plotting on the Y axes; it doesn't happen when I turn off log plotting. It also doesn't happen when I use agg.pdf driver.

Is this a well-known problem, or should I put together a little demo that demonstrates it?

Traceback (most recent call last):
   File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/matplotlib/figure.py", line 772, in draw
     for a in self.axes: a.draw(renderer)
   File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/matplotlib/axes.py", line 1601, in draw
     a.draw(renderer)
   File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/matplotlib/axis.py", line 710, in draw
     tick.draw(renderer)
   File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/matplotlib/axis.py", line 193, in draw
     self.label1.draw(renderer)
   File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/matplotlib/text.py", line 502, in draw
     ismath=ismath)
   File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/matplotlib/backends/backend_macosx.py", line 120, in draw_text
     self._draw_mathtext(gc, x, y, s, prop, angle)
   File "/Librrks/Python.framework/Versions/2.6/lib/python2.6/site-packages/matplotlib/backends/backend_macosx.py", line 112, in _draw_mathtext
     gc.draw_mathtext(x, y, angle, 255 - image.as_array())
TypeError: image has incorrect type (should be uint8)