Impala/Kudu no longer raises error on duplicate key on insert

After upgrading to CDH5.9 and the version of Impala/Kudu mentioned, it seems that an error/exception is no longer raised when trying to insert a duplicate key into a Kudu table.

For example, when using Impyla to insert a duplicate key, a Python exception used to be raised. Now no exception is raised (possibly because Impala did not return an error), and the only way to know that the record was not inserted due to duplicate key error is to read the operation log and search for "Key already present" (which you should do anyway when an exception is raised):

cur.execute("insert into table...")
op = cur._last_operation
log = op.get_log() if op else ''
print log

> Key already present in Kudu table

Was this an intentional change? It seems that key constraint violations are the sorts of things that should raise errors/exceptions.