This hotfix removes some unnecessary partition switches at initialization of bulk insert operation and improves the performance of bulk insert into partitioned cluster columnstore index (CCI).
Resolution
The issue was first fixed in the following cumulative update of SQL Server.
Cumulative Update 2 for SQL Server 2014 /en-us/help/2967546
About cumulative updates 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:
Status
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.