The date format that guides your app is the one defined in the main page
SET TimeFormat='h:mm:ss TT';
SET TimestampFormat='M/D/YYYY h:mm:ss[.fff] TT';
Try to modify that format and see what happen
Because based on what you have mentioned your date is D/M/YYYY and if you are going to ask QlikView to read it as M/D/YYYY it will only recognize it till 12/01 (because for QlikView it is Dec 1st), but 13/01 is null for QlikView because there is no 13th Month in the calendar.
Is this what you are trying to understand? Or I just made up stuff for you