move undo tablespace in RAC

DB: Oracle 11gr2

RAC: 6 nodes

Existing TS = UNDOTBS_1

NEW TS     = UNDOTBS_01

I recently created new sets of UNDO tablespace in my RAC database for each instance.

Steps:

1. Created new tablespace UNDOTBS_01

2. ALTER SYSTEM SET undo_tablespace='UNDOTBS_01' scope=BOTH;

note: I ran this statement in each instance for their respective undo tablespace.

ie. in instance 1, alter system set undo_tablespace='UNDOTBS_01' scope=BOTH;

ie. in instance 2, alter system set undo_tablespace='UNDOTBS_02' scope=BOTH;

ie. in instance 1, alter system set undo_tablespace='UNDOTBS_03' scope=BOTH;

Questions: When I bounce the instance yesterday, I see the undo_tablespace parameter changed back to old TS UNDOTBS_1.