Hello

one of the reconfigure overrides is as follows
 public virtual void Reconfigure(AbstractStore store, ColumnBase[] columns)
    {
      StringBuilder stringBuilder = new StringBuilder();
      stringBuilder.Append("[");
      foreach (ColumnBase columnBase in columns)
      {
        stringBuilder.Append(columnBase.ToConfig());
        stringBuilder.Append(",");
      }
      stringBuilder.Remove(stringBuilder.Length - 1, 1);
      stringBuilder.Append("]");
      this.Call("reconfigure", new object[2]
      {
        (object) store.ToConfig(LazyMode.Instance),
        (object) new JRawValue((object) ((object) stringBuilder).ToString())
      });
    }
see the 

(object) store.ToConfig(LazyMode.Instance),
part. the js counterpart is

reconfigure: function(store, columns) {
var me = this,
headerCt = me.headerCt;
if (me.lockable) {
me.reconfigureLockable(store, columns);
} else {
if (columns) {
delete me.scrollLeftPos;
headerCt.suspendLayouts();
headerCt.removeAll();
headerCt.add(columns);
}
if (store) {
store = Ext.StoreManager.lookup(store);
me.bindStore(store);
} else {
me.getView().refresh();
}

see the

store = Ext.StoreManager.lookup(store);

which means the lookup will be executed according the serialized store, which obviously can't work