XCode: You have updates available for other accounts

Logged in to my Mac App Store account today, the "Purchases" tab greeted me with an update for Xcode. However, clicking on it only resulted in the following:

  You have updates available for other accounts.
  Sign into the account you used to purchase it.
Huh? I don't have any other accounts. One Apple account is more than enough :-\
So, what's the deal here? (Un)fortunately, others had similar issues and a possible solution as well:
  • Delete or move /Applications/Install Xcode.app resp. Install XCode.dmg, usually found in /Applications as well. Then try again to update Xcode.

  • Refresh your Spotlight index. I.e. add/remove your system disk to the index, then try again to update:
     $ launchctl load -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist
     $ mdutil -a -i on && mdutil -a -E
    Now the AppStore should work again. Disable once the updates are completed:
     $ mdutil -a -i off
     $ launchctl unload -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist
Update: Since I have disabled Spotlight, refeshing the index would not work. Upon adding/removing items from the list of excluded directories, this happens:
 Privacy List Error
 The item couldn't be added or removed because you don't 
 have the appropriate permissions.
So we have to enable Spotlight again:
$ launchctl load -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist

$ launchctl list | grep -i metadata
5035    -       com.apple.metadata.mds
-       0       com.apple.metadata.mds.spindump
-       0       com.apple.metadata.mds.scan
Now refreshing Spotlight's index should work and AppStore will be able to install software again. We might choose to disable Spotlight again:
$ launchctl unload -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist