a mathtext bug?

Hi,

I am trying to use mathtex expression for Molecule descriptions(in the legend)

[in matplotlib-0.70.1 tkagg backend]

The following mathtext expression throws an exception in the parser.

plot(range(10))
title(r'$^{12}\rm{CO}$') # a CO molecule

The following doesn't plot the superscript part of the mathtext in the legend:
r'$\rm{CO}^{2}$

whereas this one does:

r'$CO^{2}$'

Can anyone reproduce this.

PS: Excellent plotting package! No greater pleasure than giving pgplot the
boot and replace it with something "modern".

PPS: I think this ahs come up on the mailing list earlier, but I can't quite
remember. Is it possible to tune "subplot" to do ganged plotting as in the
example script without the overhead?

Cheers,
Malte.