It's not about wx or wxpython, it's a matplotlib issue.
Let me add some color to that statement -- when I took a look at your
screenshot, I realized you are using the WX backend and not the WXAgg
backend. If you don't understand the difference, peruse
http://matplotlib.sf.net/backends.html . WXAgg may have the same
problem (and the same solution from my last post) but will give you
more consistent rendering and layout.
JDH