Extjs按需加载的问题

Extjs在使用accordion layout，总共分2个页签，每个页签都有一棵树

layout:'accordion',  
                 layoutConfig:{  
                     animate:true,
                     hideCollapseTool:true
                 },  
                 items: [{  
                     title:'导航',  
                     autoScroll:true,  
                     border:false,  
                     iconCls:'nav',  
                     html:'<div id="nav-tree" style="overflow:auto;height:400px;border:0px solid c3daf9;"></div>'
                    }  
                 ,{  
                     title:'用户设置',  
                     html: '<div id="set-tree" style="overflow:auto;height:400px;border:0px solid c3daf9;"></div>',  
                     border:false,  
                     autoScroll:true,  
                     iconCls:'settings'  
                 }]  、


//树～～～
var navtree;
		var settree;
		var sroot;
		var root;
		if(!navtree){  
	        navtree = buildTree('nav-tree');
	        root = new Ext.tree.AsyncTreeNode({  
		         text: '导航菜单',  
		         draggable:false,  
		         id:'nroot'  
		     });  
		    navtree.setRootNode(root);
	        root.appendChild(new Ext.tree.TreeNode({text:"按钮"}));
	        navtree.render();  
     		root.expand(); 
        };
        
        if(!settree){
        	settree = buildTree('set-tree');
        	sroot = new Ext.tree.AsyncTreeNode({  
		         text: '设置菜单',  
		         draggable:false,  
		         id:'sroot'  
		     });  
		    settree.setRootNode(sroot);
	        sroot.appendChild(new Ext.tree.TreeNode({text:"按钮"}));
	        settree.render();
	        sroot.expand(); 
	        settree.show();	
     		      	
        };

       function buildTree(divid){
       		 var tree = new Ext.tree.TreePanel({  
		         el:divid, 
		         //applyTo:divid, 
		         autoScroll:true,		           
		         animate:true,  
		         border:false,  
		         enableDD:true,  
		         containerScroll: true,
		         lines:false, 
		         autoShow:true,
		         rootVisible:false});
		     return tree;
       };

现在的问题是，第一棵树可以显示，第二页上的树不能显示，用firebug调试的时候，设置断点，在第二棵树显示之前用鼠标切换到第二页签，树能够正常显示？我感觉是extjs的按需加载的问题，
有什么办法能让这2棵树同时显示？？
现在暂时的解决办法是，第二棵树使用另外的方式构造，代码如下：

 if(!settree){
        	settree = new Ext.tree.TreePanel({  
		         autoShow:true,
		         autoScroll:true,		           
		         animate:true,  
		         border:false,  
		         enableDD:true,  
		         containerScroll: true,
		         lines:false, 
		         autoShow:true,
		         rootVisible:false})     	
        };
        sroot = new Ext.tree.AsyncTreeNode({  
		         text: '设置菜单',  
		         draggable:false,  
		         id:'sroot'  
		});
        settree.setRootNode(sroot);
	    sroot.appendChild(new Ext.tree.TreeNode({text:"按钮"}));
	    settree.render(Ext.get('set-tree'));
	    settree.expandAll();