One2many field issue Odoo 10.0 - postgresql

Question

I have this very weird issue with One2many field.
First let me explain you the scenario...
I have a One2many field in sale.order.line, below code will explain the structure better
class testModule(models.Model):
_name = 'test.module'
name = fields.Char()
class testModule2(models.Model):
_name = 'test.module2'
location_id = fields.Many2one('test.module')
field1 = fields.Char()
field2 = fields.Many2one('sale.order.line')
class testModule3(models.Model):
_inherit = 'sale.order.line'
test_location = fields.One2many('test.module2', 'field2')
CASE 1:
Now what is happening is that when i create a new sales order, i select the partner_id and then add a sale.order.line and inside this line i add the One2many field test_location and then i save.
CASE 2:
Create new sales order, select partner_id then add sale.order.line and inside the sale.order.line add the test_location line [close the sales order line window]. Now after the entry before hitting save i change a field say partner_id and then click save.
CASE 3:
this case is same as case 2 but with the addition that i again change the partner_id field [changes made total 2 times first of case2 and then now], then i click on save.
RESULTS
CASE 1 works fine.
CASE 2 has a issue of
odoo.sql_db: bad query: INSERT INTO "test_module2" ("id", "field2", "field1", "location_id", "create_uid", "write_uid", "create_date", "write_date") VALUES(nextval('test_module2_id_seq'), 27, 'asd', ARRAY[1, '1'], 1, 1, (now() at time zone 'UTC'), (now() at time zone 'UTC')) RETURNING id
ProgrammingError: column "location_id" is of type integer but expression is of type integer[]
LINE 1: ...VALUES(nextval('test_module2_id_seq'), 27, 'asd', ARRAY[1, '...
now for this case i put a debugger on create/write method of sale.order.line to see waht the values are getting passed..
values = {u'product_uom': 1, u'sequence': 0, u'price_unit': 885, u'product_uom_qty': 1, u'qty_invoiced': 0, u'procurement_ids': [[5]], u'qty_delivered': 0, u'qty_to_invoice': 0, u'qty_delivered_updateable': False, u'customer_lead': 0, u'analytic_tag_ids': [[5]], u'state': u'draft', u'tax_id': [[5]], u'test_location': [[5], [0, 0, {u'field1': u'asd', u'location_id': [1, u'1']}]], 'order_id': 20, u'price_subtotal': 885, u'discount': 0, u'layout_category_id': False, u'product_id': 29, u'price_total': 885, u'invoice_status': u'no', u'name': u'[CARD] Graphics Card', u'invoice_lines': [[5]]}
in the above values location_id is getting passed like u'location_id': [1, u'1']}]] which is not correct...so for this i correct the issue in code and the update the values and pass that...
CASE 3
if the user changes the field say 2 or more than 2 times then the values are
values = {u'invoice_lines': [[5]], u'procurement_ids': [[5]], u'tax_id': [[5]], u'test_location': [[5], [1, 7, {u'field1': u'asd', u'location_id': False}]], u'analytic_tag_ids': [[5]]}
here
u'location_id': False
MULTIPLE CASE
if the user does case 1 the on the same record does case 2 or case 3 then sometimes the line will be saved as field2 = Null or False in the database other values like location_id and field1 will have data but not field2
NOTE: THIS HAPPENS WITH ANY FIELD NOT ONLY PARTNER_ID FIELD ON HEADER LEVEL OF SALE ORDER
I tried debugging myself but couldn't find the reason why this is happening .