Assume that you use Microsoft SQL Server 2012 Reporting Services (SSRS 2012) Service Pack 1 (SP1) Cumulative Update 8 (CU8) or a later version. When you build a matrix with text box and use the Lookup function in its expression, duplicate records occur in the report rendering.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Article ID: 3008416 - Last Review: Jun 22, 2015 - Revision: 1
Microsoft SQL Server 2012 Service Pack 2, SQL Server 2012 Reporting Services, Microsoft SQL Server 2014 Service Pack 1, SQL Server 2014 Reporting Services