backup_label in a crash recovery

Hi,

When a crash occurs before calling pg_stop_backup(),
the subsequent crash recovery causes the FATAL error
and outputs the following HINT message.
   If you are not restoring from a backup, try removing the file
\"%s/backup_label\"."

I wonder why backup_label isn't automatically removed
in normal crash recovery case. Is this for the fail-safe
protection; prevent admin from restoring from a backup
wrongly without creating recovery.conf? Or another?

If that's intentional, a clusterware for shared disk
failover system should remove backup_label whenever
doing failover. Otherwise, when a crash occurs during
online-backup, the failover would fail.

Regards,

-- 
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center