The default values in config-main.def contain values that are specific for 
Windows. This means that the key-bindings for other platforms, such as 
OSX will be wrong (because config-main selects the windows keybindings 
as the default keybindings).

I've worked around this by copying a mac version of config-main.def over 
the installed version of config-main.def from Mac/IDLE/Makefile.in. That 
is obviously a crude hack, but I know of no better solution.