unexpected time axis limits

When I execute the script below (on Windows 10 with Python 3.5.1 and Bokeh 0.12.0), I expect the time axis of the resulting plot to extend from 18h to 6h, but instead it extends from 22h to 10h. Am I doing something wrong, or is this a Bokeh problem?

Thanks,

Harold Mills

import datetime

from bokeh.models import Range1d

from bokeh.plotting import Figure, show

start = datetime.datetime(2016, 7, 8, 18)

end = datetime.datetime(2016, 7, 9, 6)

x_range = Range1d(start=start, end=end)

y_range = Range1d(start=0, end=1)

figure = Figure(x_range=x_range, y_range=y_range)

show(figure)