How to debug an unfired tkinter event?

[jfong at ms4.hinet.net]

In last few days, I tried to experiment with the scrolling table implemented in canvas, started from this example: http://code.activestate.com/recipes/580793-tkinter-table-with-scrollbars/. Everything works fine until I moved the scrolling_area instance (which the canvas is in) from column=0 to column=1.

The canvas has a binding:
        self.canvas.bind('<Configure>', self._on_canvas_configure)

After this movement, the callback was only triggered when dragging the root widget to resize canvas vertically, but not horizontally.

Event seems has OS involved(it's MS Windows XP in my case). How to debug this kind of problem, under pdb?

Best Regards,
Jach Fong