[xubuntu] keyboard shortcuts almost all not working

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http://ubuntuforums.org – Have just completed a new install of xubuntu 12.04. I had kubuntu but have now install xubuntu on the / and left /home partition intact. I prefer to use keyboard shortcuts where possible. Strangly a few of them are working (eg. Alt+F2 & Alt+F10) but others are not (eg. Ctrl+Alt+Del & Ctrl+Esc), and changing/adding shortcuts in settings doesn't work, though if I run the relevant commands in a terminal it works. Why is this? Not sure if it's related, but the new install didn't automatically run xfwm4, though a single manual run seems to have fixed this. Thanks. (Hardware)