clip_on = False does not work for x-axis

When I set clip_on = False the curve extends beyond the y-limits, but it does not extend beyond the x-limits. Am I doing something wrong, or is this a bug?

For example, the following code:

    import matplotlib.pyplot as plt
    import numpy as np
    x1 = np.arange(-10, 10, 0.01)
    y1 = x1
    ax = plt.subplot()
    ax.set_xlim(-2,2)
    ax.set_ylim(-1,1)
    ax.plot(x1, y1, clip_on = False)

produces the plot I would expect:

![good](http://s8.postimg.org/tc0csa3p1/wtf1.jpg)

However, all I have to do is change the y-limits,

    fig = plt.figure()
    ax = plt.subplot()
    ax.set_xlim(-2,2)
    ax.set_ylim(-3,3)
    ax.plot(x1, y1, clip_on = False)

and I get the following plot:

![bad](http://s11.postimg.org/g81ef6r2b/wtf2.jpg)

Why does the first plot extend beyond the y-limits, while the second one does not extend beyond the x-limits?  In case it matters, I am using matplotlib 1.3.0 with the TkAgg backend, but apparently (http://stackoverflow.com/questions/20523752/matplotlib-clip-on-false-does-not-work-on-x-axis) it also happens with the MacOSX backend.