SQL & PL/SQL :: Missing Records While Performing Parallel Inserts

I have prepared shell scripts to do the parallel inserts on my DB table (LEGACY_SYSTEM).

There is a trigger (AFTER INSERT ON EACH ROW) associated with the above table. I am calling a package.function inside the trigger to do the required operation and finally it will insert records into my target table (PRICE_CHANGE).

Expectation:
------------
If I insert 10 rows into LEGACY_SYSTEM table, it should do few updates and finally insert 10 rows into PRICE_CHANGE table.

Result:
-------
10 rows got inserted into LEGACY_SYSTEM. All the updates are successful but I could see only 4 rows in PRICE_CHANGE table. If I run it for the second or third time, all the results will be perfect.

Instead of these shell script, if I insert one by one rows manually into LEGACY_SYSTEM table, I am getting all the expected results and the results are consistent. If you look at my scripts below, you will understand the problem better..

DRIVING SCRIPT(test_global.sh):
---------------
#!/bin/sh
./test_script.sh &
./test_script2.sh &
exit;

test_script.sh:
---------------
#!/bin/sh
./test.sh 100052051 10974 &
./test.sh 100052051 8649 &
./test.sh 100052060 10974 &
./test.sh 100052060 8649 &
./test.sh 100052078 10974 &
./test.sh 100052078 8649 &
./test.sh 100052086 10974 &
./test.sh 100052086 8649 &
exit;

test_script2.sh:
---------------
#!/bin/sh
./test.sh 100052051 11698 &
./test.sh 100052051 11777 &
./test.sh 100052060 11698 &
./test.sh 100052060 11777 &
./test.sh 100052078 11698 &
./test.sh 100052078 11777 &
./test.sh 100052086 11698 &
exit;

test.sh:
--------
#!/bin/sh
sqlplus HRUAMGR/HRUAMGR@MALDEV_DW1<<EOF
ALTER SESSION ENABLE PARALLEL DML;
insert into legacy_system (product, item, supp, type, g_ind, d_ind, o_num) values (7896544,$1,$2,'TEST',NULL,NULL,NULL);
commit;
exit;
EOF

I am calling test_global.sh through the UNIX session and all the records got inserted into LEGACY_SYSTEM table and few rows are missing from PRICE_CHANGE table.

If I remove the '&' symbol and execute, the results are perfect. But the requirement is not to remove the '&' symbol. I have been facing this problem for the past 1 month.