This is caused by an interaction between antialiasing and filled areas
with perfectly aligned edges. Both Agg and Cairo suffer from this
"problem". There has been a discussion on the devel a few times about
ways around it, none of which have really panned out, if I recall
correctly. Though t
It looks like this bug has been fixed on the SVN trunk. Unfortunately,
these changes were pretty major surgery, so they don't easily apply to
0.98.5.x. Unfortunately, for the time being, it looks like you'll need
to wait until the next release, or compile matplotlib from SVN
yourself. I have
You might be running into one of the path simplification bugs in the
0.98.x series. Have you tried with the rcParam path.simplify turned
off? If you can sent me a self contained script and data off-list, I
can test this against the SVN version to see if this has already been
addressed.
Cheer
