1.4.2 event propogation for simple button click not same as 1.3.2?

1.4.2 event propogation for simple button click not same as 1.3.2?

I have a small test case where I create a button and set its onclick hander to call my js function, followed by a "return false".  In jquery 1.3.2, when I click the button, it calls my js function.  But in in Jquery 1.4.2, it calls my js function and then does a POST, as if the return false is not there.

Here is the exact html

<html>
  <head>
    <script src="/site_media/js/jquery-1.3.2.js" type="text/javascript"></script>
    <script type="text/javascript">
      function show_input() {
        console.log("hello, world");
      }
    </script>
  </head>

  <body>
  <div id="container">
      <form autocomplete="off" action="" method="post" enctype="multipart/form-data">
      <div class="taskform_row_description form-row">
        <button id="testbutton1" onclick="show_input(); return false;">
           Test
        </button>
        <script type="text/javascript">$('#testbutton1').click();
        </script>
      </div>
      </form>
  </div>
  </body>
</html>

Could anyone tell me what I have to do in 1.4.2 to suppress the post?  I thought the "return false" is supposed to suppress the event propagation and make the post not occur?  I know there are differences betweeen 1.4 and 1.3, but this seems like a very major incompatiblity - maybe my understanding of how to do it is wrong?

Would very much appreciate any pointers, thank you!

Margie Roginski