After installing latest Mavericks update (10.9.4), keyboard keeps switching itself back to U.S.

Question

I downloaded the recommended update for OSX Mavericks 10.9.4 yesterday, and ever since, my laptop keyboard has been inexplicably switching back to U.S. every hour or so. I am based in the UK and would prefer to use the British keyboard setting, which has never been a problem in the past. However, every time I look up at my screen, my keyboard has managed to default back to U.S. at the top of my screen (next to the volume and Date and Time settings).
My laptop is late 2011 11-inch MacBook Air. Please someone help!

Answer 1

Back up all data.
This procedure will unlock all your user files (not system files) and reset their ownership, permissions, and access controls to the default. If you've intentionally set special values for those attributes on any of your files, they will be reverted. In that case, either stop here, or be prepared to recreate the settings if necessary. Do so only after verifying that those settings didn't cause the problem. If none of this is meaningful to you, you don't need to worry about it, but you do need to follow the instructions below.
Step 1
If you have more than one user, and the one in question is not an administrator, then go to Step 2.
Triple-click anywhere in the following line on this page to select it:
sudo find ~ $TMPDIR.. -exec chflags nouchg,nouappnd {} + -exec chown $UID {} + -exec chmod +rw {} + -exec chmod -N {} + -type d -exec chmod +x {} + 2>&-
Copy the selected text to the Clipboard by pressing the key combination command-C.
Launch the built-in Terminal application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad. Click Utilities, then Terminal in the icon grid.
Paste into the Terminal window by pressing command-V. I've tested these instructions only with the Safari web browser. If you use another browser, you may have to press the return key after pasting.
You'll be prompted for your login password, which won't be displayed when you type it. Type carefully and then press return. You may get a one-time warning to be careful. If you don’t have a login password, you’ll need to set one before you can run the command. If you see a message that your username "is not in the sudoers file," then you're not logged in as an administrator.
The command may take several minutes to run, depending on how many files you have. Wait for a new line ending in a dollar sign ($) to appear, then quit Terminal.
Step 2 (optional)
Take this step only if you have trouble with Step 1, if you prefer not to take it, or if it doesn't solve the problem.
Start up in Recovery mode. When the OS X Utilities screen appears, select
          Utilities ▹ Terminal
from the menu bar. A Terminal window will open. In that window, type this:
res
Press the tab key. The partial command you typed will automatically be completed to this:
resetpassword
Press return. A Reset Password window will open. You’re not going to reset a password.
Select your startup volume ("Macintosh HD," unless you gave it a different name) if not already selected.
Select your username from the menu labeled Select the user account if not already selected.
Under Reset Home Directory Permissions and ACLs, click the Reset button.
Select
           ▹ Restart
from the menu bar.