Button "Close window" doesn't work. Is it bug or feature?

When I click on button "Close window" or press <Alt+F4>, window doesn't close. Must I write my own onClose-handler?

``` go
func formOnClose(arg *gform.EventArg) {
        var sender = arg.Sender()
        w32.DestroyWindow(sender.Handler())
}

func main() {
        ... 
        mainWindow.Bind(w32.WM_CLOSE, formOnClose)
        ...
}
```

Or is there default handler?
