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We have discovered a problem in the RadGrid rendering that appears in various scenarios in Q2 2013 release. The issue appears on post back and causes broken RadGrid layout. The problematic behavior is caused by the <FilterMenu></FilterMenu> tag which is automatically added when RadGrid is created from the designer. In case the official Q2 2013 version is used in your application you need to remove the mentioned tag from the RadGrid markup in order to fix the problem.
Official fix for the presented issue is already added to the latest internal build of the controls.
Official fix for the presented issue is already added to the latest internal build of the controls.