php - Ajax only works when resending from firebug

Question

$.post(
    "ajax.php",
    { action_do:"Register" },
    function(data,status){
        alert(data);
    }
);

This script is called when the form is submitted from a page, test.php. ajax.php just echo some text.

The response body from firebug refers to test.asp ???

If I right click on the resend inside of firebug, the ajax call works, and the response body is the text from ajax.php

I am puzzled.