Could be bug in KeepTogether property. Refer to FIX: KeepTogether property does not work when you generate a report that contains a tablix in SSRS 2008 R2 or in SSRS 2012.
Symptoms
Consider the following scenario:
•You have a report that contains a tablix in Microsoft SQL Server 2008 R2 Reporting Services (SSRS 2008 R2) or in Microsoft SQL Server 2012 Reporting Services (SSRS 2012). The tablix contains a row group.
•You set the KeepTogether property to "True" and the KeepWithGroup property to "Before."
•The tablix contains a group footer.
•You try to generate the report.
In this scenario, the group is not displayed on one page. This behavior occurs because the KeepTogether property does not work correctly.
Note This issue also occurs in versions of SQL Server that were released before SQL Server 2008 R2.
Resolution
Cumulative update information
Cumulative update package 1 for SQL Server 2012 Service Pack 1
The fix for this issue was first released in Cumulative Update 1. For more information about how to obtain this cumulative update package for SQL Server 2012 Service Pack 1, click the following article number to view the article in the Microsoft Knowledge Base:
2765331
Cumulative update package 1 for SQL Server 2012 Service Pack 1Note Because the builds are cumulative, each new fix release contains all the hotfixes and all the security fixes that were included with the previous SQL Server 2012 fix release. We recommend that you consider applying the most recent fix release that contains this hotfix. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
2772858
The SQL Server 2012 builds that were released after SQL Server 2012 Service Pack 1 was released
SQL Server 2008 R2 Service Pack 2
The fix for this issue was first released in Cumulative Update 3. For more information about how to obtain this cumulative update package for SQL Server 2008 R2 Service Pack 2, click the following article number to view the article in the Microsoft Knowledge Base:
2754552
Cumulative update package 3 for SQL Server 2008 R2 Service Pack 2 Note Because the builds are cumulative, each new fix release contains all the hotfixes and all the security fixes that were included with the previous SQL Server 2008 R2 Service Pack 2 fix release. We recommend that you consider applying the most recent fix release that contains this hotfix. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
2730301
The SQL Server 2008 R2 builds that were released after SQL Server 2008 R2 Service Pack 2 was released
SQL Server 2012
The fix for this issue was first released in Cumulative Update 4. For more information about how to obtain this cumulative update package for SQL Server 2012, click the following article number to view the article in the Microsoft Knowledge Base:
2758687
Cumulative update package 4 for SQL Server 2012 Note Because the builds are cumulative, each new fix release contains all the hotfixes and all the security fixes that were included with the previous SQL Server 2012 fix release. We recommend that you consider applying the most recent fix release that contains this hotfix. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
2692828
The SQL Server 2012 builds that were released after SQL Server 2012 was released
SQL Server 2008 R2 Service Pack 1
The fix for this issue was first released in Cumulative Update 8. For more information about how to obtain this cumulative update package for SQL Server 2008 R2 Service Pack 1, click the following article number to view the article in the Microsoft Knowledge Base:
2723743
Cumulative update package 8 for SQL Server 2008 R2 Service Pack 1Note Because the builds are cumulative, each new fix release contains all the hotfixes and all the security fixes that were included with the previous SQL Server 2008 R2 Service Pack 1 fix release. We recommend that you consider applying the most recent fix release that contains this hotfix. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
2567616
The SQL Server 2008 R2 builds that were released after SQL Server 2008 R2 Service Pack 1 was released
Applies to
•Microsoft SQL Server 2008 R2 Reporting Services
•Microsoft SQL Server 2008 R2 Datacenter
•Microsoft SQL Server 2008 R2 Developer
•Microsoft SQL Server 2008 R2 Enterprise
•Microsoft SQL Server 2008 R2 Standard
•Microsoft SQL Server 2008 R2 Web
•Microsoft SQL Server 2012 Developer
•Microsoft SQL Server 2012 Enterprise
•Microsoft SQL Server 2012 Standard
•Microsoft SQL Server 2012 Web