Example animation_blit.py Sometimes Works

The title says it all. I need the simplest blit animation I can find and
when it works animation_blit.py works quite well, but sometimes it comes
up and runs to completion at almost 400 FPS, other times it comes up and
nothing is drawn at all except an empty plot.

Ubuntu Hardy
matplotlib 0.98.3
python 2.5
python-wxGtk 2.8

Any help would be appreciated.