combobox does not scroll when using keyboard

Code:

// The data store containing the list of states
var states = Ext.create('Ext.data.Store', {
    fields: ['abbr', 'name'],
    data : [
        {"abbr":"AL", "name":"Alabama"},
        {"abbr":"AK", "name":"Alaska"},
        {"abbr":"AZ", "name":"Arizona"},
        {"abbr":"AL", "name":"Alabama"},
        {"abbr":"AK", "name":"Alaska"},
        {"abbr":"AZ", "name":"Arizona"},
        {"abbr":"AL", "name":"Alabama"},
        {"abbr":"AK", "name":"Alaska"},
        {"abbr":"AZ", "name":"Arizona"},
        {"abbr":"AL", "name":"Alabama"},
        {"abbr":"AK", "name":"Alaska"},
        {"abbr":"AZ", "name":"Arizona"},
        {"abbr":"AL", "name":"Alabama"},
        {"abbr":"AK", "name":"Alaska"},
        {"abbr":"AZ", "name":"Arizona"},
        {"abbr":"AL", "name":"Alabama"},
        {"abbr":"AK", "name":"Alaska"},
        {"abbr":"AZ", "name":"Arizona"},
        {"abbr":"AL", "name":"Alabama"},
        {"abbr":"AK", "name":"Alaska"},
        {"abbr":"AZ", "name":"Arizona"},
        {"abbr":"AL", "name":"Alabama"},
        {"abbr":"AK", "name":"Alaska"},
        {"abbr":"AZ", "name":"Arizona"}
        //...
    ]
});


// Create the combo box, attached to the states data store
Ext.create('Ext.form.ComboBox', {
    fieldLabel: 'Choose State',
    store: states,
    queryMode: 'local',
    displayField: 'name',
    valueField: 'abbr',
    renderTo: Ext.getBody()
});