Oracle Database Discussions

I have four instances on my box in total. Two instances(orcl & prod) run on a file system, One instance (+Asm) is ASM storage and the last instance(test) uses the asm storage.

Following are the contents of my oratab file in /etc/oratab
orcl:/u01/oracle/software:Y
+ASM:/home/oracle/oracle/product/10.2.0/db_2:Y
test:/u01/oracle/software:Y
Prod:/u01/oracle/software:Y

Following is my db startup and shutdown script:-

ORACLE_HOME=/u01/oracle/software
ORA_OWNER=oracle

case $1 in
'start')
#If the system is starting, then .
su - $ORA_OWNER -c $ORACLE_HOME/bin/dbstart #Start the database
;;

'stop')
#If the system is stops, that is we.re shutting down our OS, then
su - $ORA_OWNER -c $ORACLE_HOME/bin/dbshut
;;
esac

When i hash out # the instances using asm in /etc/oratab (+ASM & test) the script works fine as usual i.e it will show me orcl and prod when i do a ps -ef | grep pmon , but once i un-hash all the instances in the oratab it doesnt bring up any instance on startup.

And what's funny is when i run the script manually like this su - $ORA_OWNER -c $ORACLE_HOME/bin/dbstart, it would bring up all the instances.

Not sure what the problem is, can you point it out please.