Please see my ipython notebook gist:
http://nbviewer.ipython.org/gist/pybokeh/f2aab3aafdc287d02bb8

Basically, if I try to plot_date() using x values of type datetime, I get weird errors. But if I convert the x values to type datetime.date, then it plots ok.

EDIT: the only difference between In[3] and In[4] is I used list comprehension in the plot_date() method in In[4] to convert the x values to type datetime.date.