Materialized view logs are not getting purged

Materialized view logs are not getting purged till down stream materialized views with complete refresh are done with refresh. Here is a simple test case.

SQL> create table tab1(a number primary key, b varchar2(10));

Table created.

SQL> create materialized view log on tab1;

Materialized view log created.

SQL> create materialized view mv_force refresh force as select * from tab1;

Materialized view created.

SQL> create materialized view mv_complete refresh complete as select * from tab1;

Materialized view created.

SQL> insert into tab1 select level, 'AAA' from dual connect by level <= 10;

10 rows created.

SQL> commit;

Commit complete.

SQL> exec dbms_mview.refresh('MV_FORCE');