I've started working on the missing tests for HighPage and KeysPage and also test for the functions and buttons in ConfigDialog.  That led to PR3238 because the 'help' button wasn't working.

Anyway, I found the following on http://effbot.org/tkinterbook/tkinter-events-and-bindings.htm:

"An easier solution is to prevent Tkinter from propagating the event to other handlers; just return the string “break” from your event handler:

def ignore(event):
    return "break"
text.bind("<Return>", ignore)
or

text.bind("<Return>", lambda e: "break")"

So, it seems that the 'Double-Button-1' and 'B1-Motion' bindings are to prevent those events from propagating outside of the widget.  Although, I didn't notice a difference when I commented them out, so maybe they don't have a higher level binding.