I created a trivial ST2 app in Architect 2.1 using one DataView with useComponents : true

Code:
Ext.define('MyApp.view.MyDataView', {
    extend: 'Ext.dataview.DataView',


    config: {
        defaultType: 'mydataitem',
        store: 'MyDirectStore',
        useComponents: true,
        itemConfig: {
            xtype: 'mydataitem'
        }
    }


});
and linked it to a trivial DataItem

Code:
Ext.define('MyApp.view.MyDataItem', {
    extend: 'Ext.dataview.component.DataItem'


    config: {
        padding: 10,
        layout: {
            type: 'hbox'
        },
        items: [
            {
                xtype: 'component',
                flex: 1,
                html: 'here'
            }
        ]
    },


    updateRecord: function(record) {
        // Provide an implementation to update this container's child items
    }


});
But I can only get this to work if I hand edit MyDataItem and put this line

Code:
    xtype: 'mydataitem',
in front of the config. Otherwise when I run it I get the error

Uncaught Error: [ERROR][Ext.Container#setDefaultType] Invalid defaultType of: 'mydataitem', must be a valid component xtype

Sencha Architect 2.1 won't let me put the xtype in. If I try it says

A custom config cannot override a reserved config...

However, if I hand edit the xtype property into MyDataItem, Sencha Architect removes whenever I save the project.

What should I do ?