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according to this article: http://googlewebmastercentral.blogspot.de/2012/03/upcoming-changes-in-googles-http.html
Google will - again - change it's behaviour for clicks on organic search results while being logged in to any Google service (or when using the secure search).
Could you make sure, that the tracking of "Keyword unavailable" will not be interrupted (i.e. you have a solution in place before Google implements the change).