I'm getting an issue similar to #715, except that delimiters such as (, [ and \{ work, but not others, particularly \Vert. Something like

ax.set_xlabel(r'$\left\Vert A \right\Vert$')

will crash with the same exception: Expected a delimiter (at char 5), (line:1, col:6)

Matplotlib 1.4.2 from debian sid repos