Keyboard layout changed. How and why?

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http://unix.stackexchange.com – Yesterday, I upgraded my kernel (to 3.5.0-19-generic), rebooted, and had to reinstall my video drivers to get full resolution. (After upgrading the kernel, the resolution always goes to 640x480, until I reinstall the drivers in Console Login). Now that I'm back in KDE (I didn't notice if it had changed in the Console Login), my keyboard layout has changed to the US format, so, for example Shift+2 prints @ instead of ". In KDE's System Settings -> Input Devices -> Keyboard -> Layouts, it seems to show the correct settings: Map=gb, Layout="English (UK)", Variant="English (UK, extended WinKeys (HowTos)