In Oracle, why do public synonyms become invalid when a table partition is dropped

SQL> create table part_test (
        i int primary key,
        d date
)
partition by range (d) (partition part_test_1 values less than (to_date('  2    3    4    5  1980-01-01', 'yyyy-mm-dd')));

create public synonym part_test for part_test;

select object_name, object_type, status from all_objects where object_name = 'PART_TEST';

alter table part_test add partition part_test_2 values less than (to_date('1981-01-01', 'yyyy-mm-dd'));

select object_name, object_type, status from all_objects where object_name = 'PART_TEST';

alter table part_test drop partition part_test_1;

select object_name, object_type, status from all_objects where object_name = 'PART_TEST';

drop public synonym part_test;
drop table part_test;

Table created.

SQL> SQL>
Synonym created.

SQL> SQL>
OBJECT_NAME                    OBJECT_TYPE         STATUS
------------------------------ ------------------- -------
PART_TEST                      TABLE               VALID
PART_TEST                      TABLE PARTITION     VALID
PART_TEST                      SYNONYM             VALID

SQL> SQL>
Table altered.

SQL> SQL>
OBJECT_NAME                    OBJECT_TYPE         STATUS
------------------------------ ------------------- -------
PART_TEST                      TABLE               VALID
PART_TEST                      TABLE PARTITION     VALID
PART_TEST                      TABLE PARTITION     VALID
PART_TEST                      SYNONYM             VALID

SQL> SQL>
Table altered.

SQL> SQL>
OBJECT_NAME                    OBJECT_TYPE         STATUS
------------------------------ ------------------- -------
PART_TEST                      TABLE               VALID
PART_TEST                      TABLE PARTITION     VALID
PART_TEST                      SYNONYM             INVALID

SQL> SQL>
Synonym dropped.

SQL>
Table dropped.

SQL>