Matplotlib Errorbar Caps Missing

I'm attempting to create a scatter plot with errorbars in matplotlib. The following is an example of what my code looks like:

import matplotlib.pyplot as pltimport numpy as npimport randomx = np.linspace(1,2,10)y = np.linspace(2,3,10)err = [random.uniform(0,1) for i in range(10)]plt.errorbar(x, y,       yerr=err,       marker='o',       color='k',       ecolor='k',       markerfacecolor='g',       label="series 2",       capsize=5,       linestyle='None')plt.show()

The problem is the plot which is output contains no caps at all!

For what it's worth, I'm on Ubuntu 13.04, Python 2.7.5 |Anaconda 1.6.1 (64-bit)|, and Matplotlib 1.2.1.

Could this be a hidden rcparam that needs to be overwritten?