Apologies if this is part of the migration instructions that I have missed. I'm trying to upgrade an existing 2.2.1 app to 3.0.3, and am having a problem with a fairly simple area.

I have a Toolbar on a Ext.tree.TreePanel. The toolbar has a button. The button has a tooltip.

Code:
		var btnRefresh = new Ext.Toolbar.Button (
			{
			    id:'treeRefresh',
			    text: '',
			    iconCls: 'x-btn-text x-tbar-loading',
			    tooltip:'Refresh',
			    scope: this,
			}
		);	
		
		var toolbar = new Ext.Toolbar(
			{
				items: 	[btnRefresh]
			}
		);

		tree = new Ext.tree.TreePanel(
			{
				id: 'objFileTree',
				title:'Folders',
				...
			 	bbar: toolbar,
				...
When the tree renders, I get the following failure:

this.btnEl is undefined

Reported at:

ext-all-debug.js
Line 42006 (3.0.3)

The line in question is:

Code:
this.btnEl.dom[this.tooltipType] = tooltip;
If I look at the stack in debug (Firebug), I can see that the "this" pointer points to the button, but the object does not have a "btnEl" field. It does have an "el" field however.

I've obviously missed something in the migration as this would appear to be a fairly basic feature.

I have:

Included the new CSS
Included the new images

What am I doing wrong here?