Unbinding Tkinter default bindings for Listbox

[Roger]

Hi Everyone,

I have a behavior associated with a default binding with Tkinter
Listbox that I want to get rid of but I can't no matter if I return
"break" on the binding or unbind it directly. If you have a Listbox
where the bounding box is not completely revealed in the window that
holds it and you use the mouse to drag the list box, the contents of
the listbox will move in the X direction to reveal the area that's
hidden.  After searching the internet for hours I found the behavior I
want to remove is a default binding as described here:

http://tcltk.free.fr/man/TkCmd/listbox.php3

"[3] If the mouse leaves the listbox window with button 1 down, the
window scrolls away from the mouse, making information visible that
used to be off-screen on the side of the mouse. The scrolling
continues until the mouse re-enters the window, the button is
released, or the end of the listbox is reached. "

After further searching I found that the code for this in tcl is
described here:

http://www.openmash.org/lxr/source/library/listbox.tcl?c=tk8.3

 50 bind Listbox <B1-Motion> {
 51     set tkPriv(x) %x
 52     set tkPriv(y) %y
 53     tkListboxMotion %W [%W index @%x,%y]
 54 }

Now I've found no way to successfully unbind B1-Motion from the
listbox, as I said above.  Nor return "break" on receiving the event.
I do want to eventually have my own B1-Motion binding applied to the
listbox for a different reason (with add='+' if necessary).  My next
step was to see if I could just unbind B1-Motion then programmatically
delete tkListboxMotion in my code but tkListboxMotion is not available
in the Tkinter source (it's part of a compiled binary I can't reach?).

Any help would be greatly appreciated.  Thanks!
Roger.