I installed an update on the 7th and now have some strange keyboard behaviour. After first installing the update and rebooting the keyboard layout changed to US but only for Chromium - when I checked what keyboard layout was actually in use by the system it was still UK extended winkeys and the rest of the system was using that correct layout as far as I could tell from the limited testing I did. This morning the keyboard layout is fine but I'm still having an issue where the F5 key is putting my laptop into standby rather than what it's meant to be doing which is refreshing a page. The other function keys for volume, brightness, etc. aren't working either. The F*x* keys normally make the extended function work by default and you have to hold the Fn button to make them work as traditional F*x* buttons with the exception of F5 which has no extended function but which is now putting my laptop into standby.
The laptop is a HP E2 Vision and I'm running Ubuntu 13.10 64-bit. The log in var/log/apt/history.log contains no entries for the update on the 7th but does for this morning when I ran the software updater so logging is working. I therefore don't know what was actually installed by the updater.
sudo dpkg-reconfigure keyboard-configurationin terminal and reset your keyboard layout to US (or UK if you prefer). Not writing this as an answer because I don't know if it's the cause at all, so it's just a suggestion to rule out that problem.