Database Software

I was testing different scenarios to switchover from a to b, a to c, c to b, b to c, b to a for my one primary with 2 standby configuration.

In some cases, the log_archive_dest_1 got changed.

alert .log will have those errors:

ARC7: Archiving not possible: no primary destinations
ARC7: Failed to archive thread 1 sequence 2692 (4)

drc*.log shows:
07/29/2012 02:06:37
SQL Execution error=604, sql=[ALTER SYSTEM ARCHIVE LOG CURRENT]. See error stack below.
ORA-00604: error occurred at recursive SQL level 1
ORA-16014: log 1 sequence# 2692 not archived, no available destinations
ORA-00312: online log 1 thread 1: '+DAT/prd/onlinelog/group_1.342.785963735'
ORA-00312: online log 1 thread 1: '+FRA
RSM0 failed to reset Redo Transport Services, error ORA-16778
Deferring associated archivelog destinations of sites permanently disabled due to Switchover
Notifying Oracle Clusterware to buildup primary database after SWITCHOVER
Data Guard notifying Oracle Clusterware to start services and other instances change
Command SWITCHOVER TO prdl completed

Then I checked log_archive_dest_1 it changed to standby_roles as below without db_unique_name.

log_archive_dest_1 location="USE_DB_RECOVERY_FILE_DEST", valid_for=(STANDBY_LOGFILE,STANDBY_ROLE)

Why this behavior happen? how to prevent it in real life during role transitions?

Thanks in advance.