CVS - rendering diagonal lines

I just noticed that the following script generates a diagonal line that looks
like it was drawn with a really unsteady hand:

from pylab import frange, plot, show

The problem is not noticable for a small number of points, such as
plot(frange(-1,1,.5)*1e10). I tried clearing site-packages, rebuilt MPL-0.80,
the problem appears to be in CVS.