jQuery posts error text when posting with ajax - php

Question

When I'm posting via ajax I'm sometimes getting extra characters posted for example. If the text passed though ajax yo a php $_POST I end up getting:
This is my messagejQuery127638276487364873268_374632874687326487
99% of the time posts pass though fine... I'm unsure how to capture and remove this error as it only happens some of the time.
// this is the ajax that we need to post the footprint to the wall.
$('#submitbutton').click(function () {
var footPrint = $('#footPrint').val();
var goUserId = '1';
$.ajax({
type: 'POST',
url: '/scripts/ajax-ProfileObjects.php',
data: 'do=leave_footprint&footPrint=' + footPrint + '&ref=' + goUserId + '&json=1',
dataType: 'json',
success: function(data){
var textError = data.error;
var textAction = data.action;
var textList = data.list;
if (textError == 'post_twice' || textError =='footprint_empty' || textError == 'login_req') {
// display the error.
} else {
// lets fade out the item and update the page.
}
});
return false; });

Answer 1

Try set cache to false. From http://api.jquery.com/jQuery.ajax/
cache Boolean
Default: true, false for dataType 'script' and 'jsonp'
If set to false, it will force requested pages not to be cached by the browser. Setting cache to false also appends a query string parameter, "_=[TIMESTAMP]", to the URL.

Answer 2

I found out through a process of elimination that the error was being caused by invalid data being passed to the query string.
The line:
data: 'do=leave_footprint&footPrint=' + footPrint + '&ref=' + goUserId + '&json=1',
I noticed that the footPrint variable would always break the script if '??' was passed. A number of members when asking a question would use a '??' when and not a single '?'
By wrapping the footPrint var in encodeURIComponent() I can send all the text though to the PHP script without breaking the URL string.
New Line:
data: 'do=leave_footprint&footPrint=' + encodeURIComponent(footPrint) + '&ref=' + goUserId + '&json=1',
This solution has worked for me... questions comments and suggestions still welcome.