Matplotlib v2.0.x and master on Python 3.5:

x1 = np.random.randn(100)
x2 = np.random.rand(100)
plt.hist([x1, x2], label=['x1', 'x2'], histtype='step')
plt.legend()

Actual outcome

Expected outcome

With histtype='bar' the order of the variables is preserved, as I would expect, instead of reversed, as with step.