$('div').html(""); //limpa a div

    $('div').dialog({
        resizable: false,
        height: 'auto',
        width: 400,
        modal: true,
        title: 'Criar Ticket?',
        buttons: {
            "Confirmar": function () {
                $(this).dialog("close");
                obs = prompt('Inserir alguma observação no ticket?');
                $('<input/>').attr('type', 'hidden')
                        .attr('name', "obs")
                        .attr('value', obs)
                        .appendTo('#form');
                $("#form").submit();
            },
            "Cancelar": function () {
                $(this).dialog("close");
                console.log('cancelado');
            }
        }
    });


<form action="#" id="form" method="post" accept-charset="utf-8">

<div></div>

<button id="ticket" name="obs" type="button" style="
            border-top-color: transparent;
            border-right-color: transparent;
            border-bottom-color: transparent;
            border-left-color: transparent;
            background-color: transparent;
            cursor: pointer;" title="Criar Ticket no Redmine"><img       src="https://cdn3.iconfinder.com/data/icons/fatcow/32x32/ruby_add.png" style="height: 32px" alt=""></button>
</form>