Can you include a minimal amount of code to show this? (If I am understanding this right, I think that two call to ax.text would be enough).

After #4147 was fixed, I checked if this one is also fixed, and it seems it is not. On current master, the following example produces a png, pdf and svg where the \left| and \right\rangle characters are missing around the minus signs. Furthermore, I realized that the problem is the same in the interactive backends (at least MacOSX and Qt4Agg, which are the ones I have available here).
For the plus sign, it works like expected. This is on current master.

import matplotlib
matplotlib.use('MacOSX')
import matplotlib.pyplot as plt
plt.text(0.4,0.6,r'$\left|-\right\rangle$')
plt.text(0.4,0.4,r'$\left|\minus\right\rangle$')

plt.text(0.6,0.6,r'$\left|+\right\rangle$')
plt.text(0.6,0.4,r'$\left|\plus\right\rangle$')

plt.savefig('tmp.png')
plt.savefig('tmp.pdf')
plt.savefig('tmp.svg')
plt.show()

just pinging @mdboom, @tacaswell because I'm not sure this was seen.

I assume that is a similar problem with the height of the | and > being scaled to almost zero.

This is a tricky one. At the end of the day, I think the metrics on the minus sign are just wrong (it defines a character with negative height). I guess the best we can do is special case it, but that's icky... Oh well, I think I can have a fix ready shortly.

May be worth checking whether another version of computer modern (http://www.ams.org/publications/type1-fonts, http://cm-unicode.sourceforge.net/) has better metrics.

This was actually fixed by #5871.