It looks like IDs aren't being set on form elements that specify an ID.

This:

Code:
{
                    xtype:'fieldset',
                    defaults:{
                        labelWidth:'35%',
                        listeners:{
                            change:myChangeEvent
                        }
                    },
                    items:[
                        {
                            id:'myId',
                            xtype:'numberfield',
                            name:'myMax',
                            label:'MyLabel',
//                            disabled:true,
                            disabledCls:'disabledVisible'
                        }
                    ]
                }
}
produces this in the DOM:

Code:
<input class="x-input-el x-form-field x-input-number" type="number" id="ext-element-290" name="myMax">
Ext.getCmp('myId') seems to return an element, but Ext.getCmp('myId').getValue() only returns the initial value of the numberfield.

Somehow the DOM and the ext element are de-synced.