Flat file to Sybase using SSIS

Hi there. Have a very weird problem.I am loading a flat file into Sybase db using SSIS package(tried both 2005 and 2008). Values in one of columns in flat file are 6-8 digits numbers. This column is loaded into Sybase table column with format INTEGER NOT NULL. Here comes the problem: when the destination column is NON NULLABLE somehow only first 4 digits of the values are exported. E.g. the value in the flat file is '65002343' but only 6500 appears in the destination column Or value '241209' "converted" to 2412. If I change the destination column format to be INTEGER NULLABLE or VARCHAR(25) NON NULL, then there is no problem, values are transferred without any issues. Any ideas why would this be happening and how to fix it without changing the format of the destination column?