How to solve the loading error in the Combobox interaction of Extjs4

How to solve the loading error in the Combobox interaction of Extjs4

When combobox is selected repeatedly, the lower-level Combobox will have a loading error, even though the Store data has been loaded.

You will know how to deal with the Code: (pay attention to the key statements in the red part)

},{
Xtype: 'combobox ',
LabelStyle: 'color: blue ;',
LabelWidth: 70, // label width
Width: 200, // field width
MsgTarget: 'day ',
AllowBlank: false, // whether null values are allowed
LabelStyle: 'color: red ;',
Value :'',
EmptyText: 'select a superior department .... ',
QueryMode: 'local ',
DisplayField: 'deptname ',
ValueField: 'deptname ',
Store: myUpDeptStore,
Editable: false,
TriggerAction: 'all ',
FieldLabel: "superior department ",
Listeners :{
'Select': function (combo, record, number) {// This event returns the record value of the selected item in the store. The index parameter is the Sn.
Var _ value = combo. getValue ();
Ext. getCmp ('addptcombo '). clearValue ();
Ext. getCmp ('addptcombo '). store. load ({params :{
UpDept: _ value // record [0]. data. DeptName
}
});
}
},
Name: "UpDept"
},{
Xtype: 'combobox ',
Id: 'addptcombo ',
DefaultListConfig: {// cancel the loading Mask
LoadMask: false
},
LabelStyle: 'color: blue ;',
LabelWidth: 70, // label width
Width: 200, // field width
MsgTarget: 'day ',
AllowBlank: false, // whether null values are allowed
LabelStyle: 'color: red ;',
Value :'',
EmptyText: 'select a department/team .... ',
QueryMode: 'local ',
DisplayField: 'deptname ',
ValueField: 'deptname ',
Store: myDeptStore,
Editable: false,
FieldLabel: "department ",
Name: "Dept"
}]

Note: This error should be caused by the Extjs Bug. The data has been loaded but the Mask layer has not been canceled, so we can only remove it manually.