Assume that you enable the C2 audit tracing by setting the "C2 Audit mode" option to 1 with sp_configure in Microsoft SQL Server 2012 or SQL Server 2014. After you restart SQL Server for the first time, "C2 Audit mode" option cannot be enabled. However, after you restart SQL Server one more time, the C2 audit tracing works correctly.
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Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.