I found there are some similar issues, I would recommend to submit it to the Microsoft Connect at this link https://connect.microsoft.com/SQLServer/Feedback. This connect site will serve as a connecting point between you and Microsoft, and ultimately the large community for you and Microsoft to interact with. Your feedback enables Microsoft to offer the best software and deliver superior services, meanwhile you can learn more about and contribute to the exciting projects on Microsoft Connect.
Sum of operator costs is more than 100% (in the execution plans)
Execution Plan Estimated Operator Cost
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Best Regards,Uri Dimant SQL Server MVP, http://sqlblog.com/blogs/uri_dimant/
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there are a few known issues with the costs as indicated below, however these are just estimated costs so you shouldn't place too much emphasis on them. If your clustered index seek cost is 100% or 96.99% it's still worth a look right?