如何完成向USB设备发送命令？

I've written some code in Go to control a USB device (see below).

Now the weird behavior is this, the code executes correctly en does what it should do on the device. The commands I send to the device afterward though, do not get executed. Why is that? If I remove the USB device and plug it back in, same behavior. I can just execute one command.

It seems that I'm misunderstanding a basic concept about USB. Should I close the connection or so?

func main() {

    // get Flags and set custom variables if needed
    rawCOM := flag.Int64("command", 101, "Set a command based Based on the commands: http://www.robot-electronics.co.uk/htm/usb_rly08btech.htm")
    rawVID := flag.Int64("vid", 0x04d8, "Add the VID of the usb device.")
    rawPID := flag.Int64("pid", 0xffee, "Add the PID of the usb device.")
    flag.Parse()

    // get COM (= command)
    COM := gousb.ID(*rawCOM)

    // get VID
    VID := gousb.ID(*rawVID)
    log.Println("Running with VID: ", VID)

    // get PID
    PID := gousb.ID(*rawPID)
    log.Println("Running with PID: ", PID)

    // Based on the commands: http://www.robot-electronics.co.uk/htm/usb_rly08btech.htm
    data := make([]byte, 5)
    data[0] = byte(COM) // see command list from url

    // Initialize a new Context.
    ctx := gousb.NewContext()
    defer ctx.Close()

    // Open any device with a given VID/PID using a convenience function.
    // found via: `$ system_profiler -xml SPUSBDataType``
    dev, err := ctx.OpenDeviceWithVIDPID(VID, PID)
    if err != nil {
        log.Fatalf("Could not open a device: %v", err)
    }
    defer dev.Close()

    // Switch the configuration to #1.
    cfg, err := dev.Config(1)
    if err != nil {
        log.Fatalf("%s.Config(1): %v", dev, err)
    }
    defer cfg.Close()

    // In the config #1, claim interface #1 with alt setting #0.
    intf, err := cfg.Interface(1, 0)
    if err != nil {
        log.Fatalf("%s.Interface(1, 0): %v", cfg, err)
    }
    defer intf.Close()

    // set writing endpoint
    ep, err := intf.OutEndpoint(0x02)
    if err != nil {
        log.Fatalf("%s.OutEndpoint(2): %v", intf, err)
    }

    // Write data to the USB device.
    numBytes, err := ep.Write(data)

    // check if success
    if numBytes != 5 {
        log.Fatalf("%s.Write([5]): only %d bytes written, returned error is %v", ep, numBytes, err)
    }

    log.Println("Command ", COM, " delivered successful")

}