UI issue with Window Manager config

[Chris Angelico]

Not sure if this would be called a "bug" or not, so I'll ask about it here.

In the Window Manager config, Keyboard tab, the "Clear" and "Close"
buttons (one inside the tab, one outside) both have shortcut Alt-C.
This means that there's no quick way to clear a bunch of keyboard
shortcuts (g Ctrl-F1 through F12, by default switching to different
workspaces - I want them to go through to the application); I have to
either click with the mouse, or hit Alt-C, Alt-C, Space. Can one of
them be changed in key? Is this a simple tweakable?

Debian Wheezy, Xfce 4.8

ChrisA