This must be a simple one but got no idea why is this happening.
Under this query:
INSERT INTO assist_reg (ar_id,ar_subid,ar_date) VALUES ('','2431052014','2014-05-31');
Field ar_subid on DDBB always records this value you can see on this screenshot:
ar_subid is a INT field with maximum of 20 characters, non-null with no predeterminate valur. this table is under UTF8-generalci.