With the Mac OS X backend, under certain conditions, I guess tons of error messages like:

Oct 17 15:47:38 weinberg.local Python[877] <Error>: CGContextClosePath: no current point.

when I move the mouse inside a sliderand when the figure is first drawn (it contains many plots). The TkAgg backend does not report any problem.

This slows down considerably the interaction with the slider.

The code is currently complex, so sharing it here is not obvious: are there tests, changes, etc. that I could run so as to try to nail down the problem?