Please try this code to solve your issue.
$('#dg').datagrid({
onBeforeSortColumn: function(){
var opts = $(this).datagrid('options');
if (opts.sorting){
return false;
}
opts.sorting = true;
},
onSortColumn: function(){
var opts = $(this).datagrid('options');
setTimeout(function(){
opts.sorting = false;
},400);
}
})