Form in modal dialog submits on enter keypress if only one field present

Bizarre, I know.

I created a form with one visible field as follows:

<div id="addkeyword" style="display: none;" title="Quick-Add a Keyword">

<form action="null.php" method="POST" id="addkeywordform">

<div>

<input type="hidden" name="obj" value="KWD">

<input type="hidden" name="fnc" value="ADD">

<input type="hidden" name="ctx" value="CAS">

</div>

<table>

<tr><td id="addkeyword-keywordprompt">Keyword<td><input type="text" name="keyword" id="addkeyword-keyword" style="width: 250px;">

</table>

</form>

</div>

I set this up as a modal dialog box that is called when a user selects the embedded option "(quick-add)" from an autocomplete text field in a prior form as follows:

function keywordSelectHandler(event,ui,objArray,elementstub,title) {

$('#'+elementstub).val('');

if (ui.item.name == 'ADD') {

$('#addkeyword-keyword').val('');

$('#keywords').val('');

$("#addkeyword").dialog({minWidth: 400, modal: true, title: title,

draggable: false, resizable: false,

buttons: {

"Submit": function() {

var validated = true;

if ($('#addkeyword-keyword').val() == '') {

validated = false;

$('#addkeyword-keywordprompt').css('color','red');

}

if (validated) {

$.ajax({

url: '/ajaxform.php',

type: 'POST',

dataType: 'json',

data: ($('#addkeywordform').serialize()),

error: function() {

alert('something went wrong');

},

success: function(json) {

var messages = $('#messages');

if (json[0] == 'error') {

messages.attr('title','error!');

messages.html(json[1]);

messages.dialog({

modal: true

});

}

if (json[0] == 'ok') {

ui.item.name = json[1];

ui.item.shortform = json[2];

ui.item.value = json[2]+' ('+json[3]+')';

ui.item.blinky = true;

addobjtolist(ui,objArray,elementstub);

ui.item.name = 'ADD';

$('#addkeyword').dialog("close");

}

}

});

}

},

Cancel: function() {

$(this).dialog("close");

$('#'+elementstub).focus();

}

},

close: function() {

$('#'+elementstub).focus();

}

});

} else {

addobjtolist(ui,objArray,elementstub);

}

$('#'+elementstub).val('');

return false;

}

If the user hits the enter key while focused on the "keyword" field in the modal dialog, the form submits.

If, however, I add the following to the initial form declaration

<tr style="display: none"><td>(unused)<td><input type="text" name="neverused-jqueryui_may_have_bugs">

the form does not submit when the enter key is pressed.

This may well be because of my poor coding skills -- I don't really know what I'm doing.

Occurs in Firefox 3.6.13, Opera 11.0. Haven't tested other browsers.