latex ' (prime)

Observe the following image:

import pylab
pylab.plot([0,1],[1,2],label="$\sigma'_0$")
pylab.legend()
pylab.savefig('test.png')

Notice that the \prime introduced by the single quote in the legend is not raised above the \sigma, like it would be in TeX (i.e., in TeX, $\sigma'_0$ is equivalent to $\sigma^\prime_0$, IIRC). Is this a design decision, or is it easy to fix? This is with matplotlib 1.0.0.

Thanks,

Jason