BUG #14143: stop database with -m immediate cause fatal message log when database start

The following bug has been logged on the website:

Bug reference: 14143
Logged by: marc hsiao
Email address: marc47marc47(at)gmail(dot)com
PostgreSQL version: 9.6beta1
Operating system: Centos 5.4
Description:

The database start with FATAL message when I try to stop the database with
immediate.
I assume that FATAL, is a critical error log, it should be an warning
only.

My application will not continue when database has FATAL log in starting
progress.

[dbsecure(at)rd4 (SecuCenter_) SecureCenter]$pg_ctl stop -m immediate
waiting for server to shut down....LOG: received immediate shutdown
request
WARNING: terminating connection because of crash of another server
process
DETAIL: The postmaster has commanded this server process to roll back the
current transaction and exit, because another server process exited
abnormally and possibly corrupted shared memory.
HINT: In a moment you should be able to reconnect to the database and
repeat your command.
LOG: database system is shut down
done
server stopped
[dbsecure(at)rd4 (SecuCenter_) SecureCenter]$pg_ctl -D ./data -w start
waiting for server to start....LOG: database system was interrupted; last
known up at 2016-05-17 12:03:09 CST
FATAL: the database system is starting up
.LOG: database system was not properly shut down; automatic recovery in
progress
LOG: invalid record length at 0/7A5F770: wanted 24, got 0
LOG: redo is not required
LOG: MultiXact member wraparound protections are now enabled
LOG: autovacuum launcher started
LOG: database system is ready to accept connections
done
server started