Label text alignment problem?

Hello again,

     I've created some axes, and I'm trying to put some custom Ox tick
labels on the axes. I would also like to have different alignments for
each tick label. This is the code I'm using (with matplotlib.0.61.0a
on Win32 with the WXAgg backend):

        self.axes.set_xticks( [0, 1, 2, 3 ])
        th = self.axes.set_xticklabels( ['12:23:000', '+4s', '+8s', '+12s' ] )
        th[ 0 ].set_horizontalalignment( 'left' )
        th[ 1 ].set_horizontalalignment( 'center' )
        th[ 2 ].set_horizontalalignment( 'center' )
        th[ 3 ].set_horizontalalignment( 'right' )

    But it seems that all the tick labels have the last set alignment
(in this case 'right'). Is this a bug, or am I just missing something
as usual?
    Thank you.