You should dispatch event and use following snippet to keep inputs behaviour:
DEMO jsFiddle
function aa() {
$("#sortable").sortable({
start: function (event, ui) {
$(this).data('preventBehaviour', true);
}
});
$("#sortable :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('li')[0].dispatchEvent(mdown);
}).on('click', function (e) {
var $sortable = $("#sortable");
if ($sortable.data("preventBehaviour")) {
e.preventDefault();
$sortable.data("preventBehaviour", false)
}
});
}