I'm aware that the built in mathtext rendered is not expected to be perfectly identical to tex, but I'm seeing some egregious behavior with spacing that I cannot seem to explain. With:

import matplotlib.pyplot as plt
plt.figure()
plt.figtext(0.1, 0.9, r"1. ($a^2$)", size=20)
plt.figtext(0.1, 0.8, r"2. $(a^2)$", size=20)
plt.figtext(0.1, 0.7, r"3. $\left(a^2\right)$", size=20)
plt.show()

In both 1.4.2 and a recent development version I get a rogue space before the bracket in all three cases:

Compared with turning text.usetex on:

Using a negative space (\!) fixes the issue rendering with matplotlib, but screws up the latex output.