tkinter: invisible PanedWindow "sashes" on OS X

[Arnaud Delobelle]

Hi Python List,

I'm trying to use PanedWindow on OS X (10.8.3).  I've started with the
effbot docs example (http://effbot.org/tkinterbook/panedwindow.htm),
namely:

----------
from Tkinter import *

m = PanedWindow(orient=VERTICAL)
m.pack(fill=BOTH, expand=1)

top = Label(m, text="top pane")
m.add(top)

bottom = Label(m, text="bottom pane")
m.add(bottom)

mainloop()
----------

I can see two panes alright, but no handle to resize them (or 'sash'
as they seem to be called in tkinter).  Is there something else that I
should be doing?

TIA,

-- 
Arnaud