Keyboard Shortcuts and the "alt" key

[Chris Metcalf <chrismetcalf gmail com>]

I'm trying to set up some keyboard shortcuts, but I'm having troubles
getting the "Keyboard Shortcuts" editor to recognize the "Alt" key as
a modifier.

I want to use arrow keys, along with the alt and control keys held
down, to switch workspaces. But when I try and set up a shortcut like
<Control><Alt>Up, it instead is set as <Control>Alt_L or
<Control>Alt_R depending on which Alt key I press. How can I convince
the Keyboard Shortcuts editor that I want to use Alt as a modifier and
not as a key?

I'm using the Generic 101-key keyboard map.

Thanks,
-- 
Chris Metcalf
chris chrismetcalf net
http://chrismetcalf.net