rot parameter ignored in line plot

[CRP]

a=DataFrame(randn(10,2),index=range(10,100,9),columns=('a','b'))

a.plot(rot=30)
Out[67]: <matplotlib.axes.AxesSubplot at 0x11e4eaa90>

the resulting chart's xaxis ticklabels remain unrotated. (pandas 0.8.1)