viewport off-by-one error?

I noticed that when plotting sine waves ( for example)
with the gtk backend that the lowest points are not plotted.

So I wrote a test script to plot a square, the result is that the left
and top edges are plotted and the bottom and right edges are clipped off
(I can pan the view to display the missing lines). I can't think of any
reason why you would plot data points and then expect them to be clipped
off, so to me it looks like an off-by-one error.

Test program:

from matplotlib.matlab import *

x = arange(0, 10+1, 1)
plot(x, x*0+10, 'r-',
     x, x*0, 'r-',
     x*0, x, 'r-',
     x*0+10, x, 'r-')