OnChange Not Firing When Input Is Populated?

I have a date selector that populates an input box. My input box looks like:

Code:
<input type="text" name="date_input" id="date_input" onchange="this.form.submit()">
<script language="JavaScript">
new tcal ({
'formname': 'make_graph',
'controlname': 'date_input'
});

Now, when the input box is populated, the onsubmit doesnt trigger. I have tried adding the following to the end of the javascript file for the date selection, but it has no effect:

[Code]...