Comment 30 for bug 214786

Confirmed on Ubuntu 9.04 with Danish alu keyboard.

You can work around it by issuing the command:
xmodmap -e 'keycode 94=onehalf section' -e 'keycode 49=less greater backslash brokenbar backslash brokenbar'

or follow the guide at https://help.ubuntu.com/community/AppleKeyboard to add it upon startup.