You need to dispatch event because jQuery UI draggable prevent drag behaviour on input element. Now, to still have input element responsive, you can use following workaround:
DEMO jsFiddle
$(".draggable").draggable({
start: function( event, ui ) {
$(this).data('preventBehaviour', true);
}
});
$(".draggable :input").on('mousedown', function (e) {
var mdown = document.createEvent("MouseEvents");
mdown.initMouseEvent("mousedown", true, true, window, 0, e.screenX, e.screenY, e.clientX, e.clientY, true, false, false, true, 0, null);
$(this).closest('.draggable')[0].dispatchEvent(mdown);
}).on('click', function(e){
var $draggable = $(this).closest('.draggable');
if($draggable.data("preventBehaviour")){
e.preventDefault();
$draggable.data("preventBehaviour", false)
}
});