ORA-01548: active rollback segment ‘_SYSSMU1_xxxx’ found, terminate dropping tablespace while deleting UNDOTBS1

Scenerio

Oracle Database 12c Standard Edition Release 12.1.0.2.0 - 64bit Production.

Database - In No archivelog Mode.

Red Hat Enterprise Linux Server release 6.5 (Santiago)

SQL> drop tablespace UNDOTBS1 including contents;

drop tablespace UNDOTBS1 including contents

*

ERROR at line 1:

ORA-01548: active rollback segment '_SYSSMU1_1255349037$' found, terminate dropping tablespace

Workaround
SQL> CREATE UNDO TABLESPACE UNDOTBS DATAFILE '/database/as3phc/undo01.dbf' size 500m autoextend off;

SQL> ALTER SYSTEM SET UNDO_TABLESPACE = undotbs;

SQL> drop tablespace UNDOTBS01 including contents;

drop tablespace UNDOTBS01 including contents

*

ERROR at line 1:

ORA-01548: active rollback segment '_SYSSMU1_1255349037$' found, terminate dropping tablespace

SQL> drop rollback segment '_SYSSMU1_1255349037$';

drop rollback segment '_SYSSMU1_1255349037$'

*

ERROR at line 1:

ORA-02175: invalid rollback segment name

SQL> select segment_name, status, tablespace_name from dba_rollback_segs;

SEGMENT_NAME               STATUS                                 TABLESPACE_NAME

-----------------------------------------------------------------------------------------------------

SYSTEM                                ONLINE                                 SYSTEM

_SYSSMU1_3780397527$    PARTLY AVAILABLE        UNDOTBS1

...

...

SQL> alter system set "_offline_rollback_segments="_SYSSMU1_1255349037$" scope=spfile;

SQL> Shutdown immediate;

SQL> Startup

SQL> select segment_name, status, tablespace_name from dba_rollback_segs;

SEGMENT_NAME               STATUS                                 TABLESPACE_NAME

-----------------------------------------------------------------------------------------------------

SYSTEM                                ONLINE                                 SYSTEM

_SYSSMU1_1255349037$   NEEDS RECOVERY                        UNDOTBS1

...

...

SQL> drop tablespace UNDOTBS1 including contents and datafiles;

drop tablespace UNDOTBS1 including contents and datafiles

*

ERROR at line 1:

ORA-01548: active rollback segment '_SYSSMU1_1255349037$' found, terminate

dropping tablespace

SQL> drop rollback segment "_SYSSMU1_1255349037$";

Rollback segment dropped.

SQL> drop tablespace UNDOTBS1 including contents and datafiles;

Tablespace dropped.

SQL> alter system reset "_offline_rollback_segments" scope=spfile;

SQL> shut immediate;

SQL> Startup

SQL> select segment_name,status,tablespace_name from dba_rollback_segs;

SEGMENT_NAME               STATUS        TABLESPACE_NAME

---------------------------------------------------------------------------------------------

SYSTEM                                ONLINE         SYSTEM

_SYSSMU1_1266566787$    ONLINE        UNDOTBS

...

...

...

_______________________________________________________________________

Note : Ideas & Inspirations