When you run a query that tries to spill more than 65,535 extents to the tempdb database, an numeric overflow occurs. Therefore, an incorrect is returned.
This issue occurs because you can't read all the extents back after overflow.
Cumulative update information
The issue was first fixed in the following cumulative update of SQL Server:
Each new cumulative update for SQL Server contains all the hotfixes and all the security fixes that were included with the previous cumulative update. We recommend that you download and install the latest cumulative updates for SQL Server 2014:
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.