RMAN won't delete archivelog

We have oracle version 11.2.0.2.

I set the rman config for the archive log retention as follows:

CONFIGURE RETENTION POLICY TO RECOVERY WINDOW OF 60 DAYS;

CONFIGURE ARCHIVELOG DELETION POLICY TO BACKED UP 2 TIMES TO DISK;

And following is my backup scripts:

RUN {

BACKUP
   FULL
   TAG Daily_Full_Backup
   DATABASE
   ;
BACKUP
   CURRENT CONTROLFILE
   ;
SQL 'alter system archive log current';
BACKUP
   ARCHIVELOG ALL FORMAT '/dxibackup/%d_%t_%s_%p.arch';

DELETE NOPROMPT OBSOLETE;
CROSSCHECK BACKUP;
CROSSCHECK ARCHIVELOG ALL;
DELETE NOPROMPT EXPIRED BACKUP;
DELETE NOPROMPT EXPIRED ARCHIVELOG ALL;

}

However, after two backups rman still didn't clear up the archive logs. I see in the backup log output that the backup skipped any archivelogs that have backed up for 2 times already.