"INSERT INTO" overwrite old data when destination table encapsulated by backquote

create database tdb;
use tdb;
create table t1(id int);
create table t2(id int);
explain insert into `tdb.t1` select * from t2;

+---------------------------------------------------------------------------------------------------------------------------------------------------+
|                                                                      Explain                                                                      |
+---------------------------------------------------------------------------------------------------------------------------------------------------+
| STAGE DEPENDENCIES:                                                                                                                               |
|   Stage-1 is a root stage                                                                                                                         |
|   Stage-6 depends on stages: Stage-1 , consists of Stage-3, Stage-2, Stage-4                                                                      |
|   Stage-3                                                                                                                                         |
|   Stage-0 depends on stages: Stage-3, Stage-2, Stage-5                                                                                            |
|   Stage-2                                                                                                                                         |
|   Stage-4                                                                                                                                         |
|   Stage-5 depends on stages: Stage-4                                                                                                              |
|                                                                                                                                                   |
| STAGE PLANS:                                                                                                                                      |
|   Stage: Stage-1                                                                                                                                  |
|     Map Reduce                                                                                                                                    |
|       Map Operator Tree:                                                                                                                          |
|           TableScan                                                                                                                               |
|             alias: t2                                                                                                                             |
|             Statistics: Num rows: 0 Data size: 0 Basic stats: NONE Column stats: NONE                                                             |
|             Select Operator                                                                                                                       |
|               expressions: id (type: int)                                                                                                         |
|               outputColumnNames: _col0                                                                                                            |
|               Statistics: Num rows: 0 Data size: 0 Basic stats: NONE Column stats: NONE                                                           |
|               File Output Operator                                                                                                                |
|                 compressed: false                                                                                                                 |
|                 Statistics: Num rows: 0 Data size: 0 Basic stats: NONE Column stats: NONE                                                         |
|                 table:                                                                                                                            |
|                     input format: org.apache.hadoop.hive.ql.io.RCFileInputFormat                                                                  |
|                     output format: org.apache.hadoop.hive.ql.io.RCFileOutputFormat                                                                |
|                     serde: org.apache.hadoop.hive.serde2.columnar.ColumnarSerDe                                                                   |
|                     name: tdb.t1                                                                                                                  |
|                                                                                                                                                   |
|   Stage: Stage-6                                                                                                                                  |
|     Conditional Operator                                                                                                                          |
|                                                                                                                                                   |
|   Stage: Stage-3                                                                                                                                  |
|     Move Operator                                                                                                                                 |
|       files:                                                                                                                                      |
|           hdfs directory: true                                                                                                                    |
|           destination: hdfs://hacluster/user/hive/warehouse/tdb.db/t1/.hive-staging_hive_2017-06-15_15-52-34_017_849305017872068583-1/-ext-10000  |
|                                                                                                                                                   |
|   Stage: Stage-0                                                                                                                                  |
|     Move Operator                                                                                                                                 |
|       tables:                                                                                                                                     |
|           replace: true                                                                                                                           |
|           table:                                                                                                                                  |
|               input format: org.apache.hadoop.hive.ql.io.RCFileInputFormat                                                                        |
|               output format: org.apache.hadoop.hive.ql.io.RCFileOutputFormat                                                                      |
|               serde: org.apache.hadoop.hive.serde2.columnar.ColumnarSerDe                                                                         |
|               name: tdb.t1                                                                                                                        |
|                                                                                                                                                   |
|   Stage: Stage-2                                                                                                                                  |
|     Merge File Operator                                                                                                                           |
|       Map Operator Tree:                                                                                                                          |
|           RCFile Merge Operator                                                                                                                   |
|       merge level: block                                                                                                                          |
|       input format: org.apache.hadoop.hive.ql.io.RCFileInputFormat                                                                                |
|                                                                                                                                                   |
|   Stage: Stage-4                                                                                                                                  |
|     Merge File Operator                                                                                                                           |
|       Map Operator Tree:                                                                                                                          |
|           RCFile Merge Operator                                                                                                                   |
|       merge level: block                                                                                                                          |
|       input format: org.apache.hadoop.hive.ql.io.RCFileInputFormat                                                                                |
|                                                                                                                                                   |
|   Stage: Stage-5                                                                                                                                  |
|     Move Operator                                                                                                                                 |
|       files:                                                                                                                                      |
|           hdfs directory: true                                                                                                                    |
|           destination: hdfs://hacluster/user/hive/warehouse/tdb.db/t1/.hive-staging_hive_2017-06-15_15-52-34_017_849305017872068583-1/-ext-10000  |
|                                                                                                                                                   |
+---------------------------------------------------------------------------------------------------------------------------------------------------+