What could be causing this?
This code DOES NOT work

var centerPanel = Ext.getCmp('centerPanel');
var centerRegion = Ext.getCmp('centerRegion');
centerRegion.remove(centerPanel, true);
centerRegion.add(centerItem);

centerRegion.doLayout();

//this code removes the item from the container - based on Firebug
centerRegion.remove(centerPanel, true);

//...but this code STILL shows the item
centerRegion.doLayout();