Do not know if this is the right place because it is not a bug in the library but in the examples.
Tried to run the examplehttp://matplotlib.org/examples/misc/multiprocess.html and I think it would be good to make the following changes:

remove dependencies to gobject

matplotlib.use('GtkAgg')

import gobject

return return call_back()
instead of return call_back

use different timer

self.gid = gobject.timeout_add(1000, self.poll_draw())

timer = self.fig.canvas.new_timer(interval=1000)
timer.add_callback(self.poll_draw)
timer.start()

Cheers,
Thomas