How to Resolve ORA-16009: remote archive log destination must be a STANDBY database

Saw an error in the alert log.
... Sat Mar 21 10:28:48 2015
Errors in file /oracle/admin/ORCL/bdump/orcl_arc0_9548203.trc:
ORA-16009: remote archive log destination must be a STANDBY database
There may be a misunderstanding between the primary and the standby databases, we could have two primary databases with the same database name in the same time.

I know that's essentially wrong to have two primary databases in the same data guard environment. Somehow, you may activate the standby database to the primary role for a short time for some reasons.

The workaround is to defer the transportation on both sides.
SQL> alter system set log_archive_dest_state_2=defer scope=memory;