jQuery .post gets null data

This is my first post here, so I hope I'm doing it appropriately.

I have several jQuery $.post calls that work just fine. They send data to a PHP script that modifies a database and returns some data. No problem.

But this one doesn't work. The returned data is just NULL.

$.post("act_addTaskLog.php",
 {description: $("#logFormDescription").val(), complete: $("#logFormComplete").is(':checked'), taskId: $("#logFormTaskId").val(), user: <?php echo $_SESSION['user']; ?>},
 function(data) {
  alert("data: " + data);
 }
);
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I've tried everything I can think of, to no avail. I've even tried just one line in my PHP script:

die("true");

Firebug shows that the script is being executed, but it's not completing. The alert message displays just with the label "data:" in it, no actual data.

Thanks in advance for your help!

I feel like an idiot now. The problem was outside the code I posted here.

The $.post call is being made as the button action on a Dialog. I added a keydown listener for the Dialog (in the "open" method), so it would submit when Enter is pressed.

For some reason, pressing Enter reloaded the entire page. So I added this line to my keydown listener code:

window.stop();

That line was causing my problems with the callback data. Removing it fixed this issue. My actual $.post code was just fine.