Handling pick events does not work on logarithmic axes. See the example below. As long as the line statement ax.set_xscale('log') is commented out, clicking on the polygons created by axvspan xauses them to change from gray to red. Uncomment that line to make the x axis logarithmic, and clicking on the polygons has either no effect or is misdirected to the far-left polygon only.

    from matplotlib import pyplot as plt
    fig = plt.figure()
    ax = fig.add_subplot(111)
    ax.set_xlim(1, 10)
    for i in range(1, 10, 3):
        ax.axvspan(i, i + 1, color='gray', picker=True)

    # uncomment this line to break the picker
    # ax.set_xscale('log')

    def onpick(event):
        event.artist.set_color('red')
        fig.canvas.draw()

    fig.canvas.mpl_connect('pick_event', onpick)
    plt.show()

Tested on version 1.4.0 and master as of 04496b0 on Mac OS X Mavericks.

[TAC edited for formatting]