Assume that you use a Multidimensional instance of SQL Server 2012 Analysis Services. After you ProcessUpdate a dimension, the Multidimensional Expressions (MDX) LastChild function may return incorrect result.
This problem was fixed in the following cumulative update for 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. Check out the latest cumulative updates for SQL Server: