Two Scale Problem with ticks on secondary axis?

When I run the example for two scales (, the secondary axis - on the right- has ticks for both scales. The primary - on left - has the expected one set of ticks.
I did modify the example code as shown below. Instead of calling the twinx function of pylab I explicitly took the code from this was because I wanted to see exactly what was being done with an intent to modify it slightly. In any case it should be completely equivalent to the example. When I did run the example unchanged it gave the same result.

Is this a bug or something I am missing something ?

Running matplotlib 0.84 on OS X 10.3.9

import pylab
import Numeric
N = Numeric
PL = pylab

ax1 = PL.subplot(111)
t = N.arange(0.01, 10.0, 0.01)
s1 = N.exp(t)
PL.plot(t, s1, 'b-')
PL.xlabel('time (s)')
# turn off the 2nd axes rectangle with frameon kwarg
#ax2 = PL.twinx()
ax = PL.gca()
ax2 = PL.gcf().add_axes(ax.get_position(), sharex=ax, frameon=False)

s2 = N.sin(2*N.pi*t)
PL.plot(t, s2, 'r.')