The bpstart_notify and bpend_notify scripts do not get called during a SQL database backup.
This issue is related to a limitation of the DBBACKUP.EXE process. During SQL backups, DBBACKUP.EXE is the process responsible for the backups. This process does not have the capability of calling thebpstart_notify and bpend_notify scripts; therefore, the scripts will fail to execute.
I know that the MS Admins here have something inline with the backup job that shrinks/truncates the logs for all SQL backups when run successfully. If the backup fails then they run a log job that backups the logs and then shrinks them. Normally the log job is scheduled to start half an hour after the SQL job and closes the window two hours before the SQL job normally completes. That way if it does fail the SQL Server does not have issues with huge logs.