ExtJS FieldSet fieldLabel doesn't show in FormPanel

I have a FormPanel with several textfield items and a fieldset that contains a combobox and a button. The fieldset has a column layout in order to make the combobox and button display side-by-side. However, the fieldset's field label does not display, even though it is inside a FormPanel. When I make the fieldset's layout form, only the label separator appears. Why is this happening? Is there a better way to have a form with several textfields and then a combobox and button side-by-side?

Here's what I have:

this.searchPanel = new Ext.FormPanel({
    border: false,
    frame: true,
    style:  'width:50%',
    bodyStyle: 'padding:6px 10px 0px 10px',
    items: [{
        //Several textfields
        },{
            xtype: 'fieldset',
            border: false,
            autoHeight: true,
            fieldLabel: 'Sort by',
            labelStyle: 'font-weight: normal',
            style: 'padding:0;margin-bottom:0',
            layout: 'column',
            items: [
                {
             开发者_Go百科       xtype: 'combo',
                    name: 'sort',
                    style: 'width:100%',
                    columnWidth: .5,
                    hiddenName: 'sort',
                    store: //Commented out for brevity
                    mode: 'local',
                    editable: false,
                    forceSelection: true,
                    triggerAction: 'all'
                },{
                    xtype: 'button',
                    style: 'margin-left: 10px',
                    columnWidth: .5
                }
            ]
        }
    ]
});

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FieldSet's do not have a fieldLabel like other form components, instead they have a title like a panel.