Confirmed. I have the same error with your script (Yikes!). And, the
error doesn't appear on the unstable version. So, it's time to do some
bug-hunting!
I'll get in touch with the matplotlib maintainers and see where the
mistake could be, if I can't figure it out myself.
For now, I suggest a workaround. Add this to the top of the code, you
can add the following to force TeX use:
rc('text', usetex=True)
Please tell me if this helps. I shall probe further then.