The typical columnstore table is usually large and contains hundreds of millions or even billions of rows. Think about large fact tables in the data warehouses or huge transactional tables in OLTP systems. Those tables are usually partitioned. Besides usual reasons (Availability, Maintainability, etc), partitioning helps with the data load – it is easier to perform ETL in the staging table and import data through partition switch.
And here comes the problem. If you run OLTP query against partitioned clustered columnstore table and end up with the execution plan that uses index intersection of nonclustered B-Tree indexes, you may get incorrect results.
Getting the correct results in a query is pretty important (he says, with understatement), so this is an important bugfix; keep those SQL Server instances patched accordingly.