Alain,
you are so right, this is not happening on ArduinoMega2560
I had a ArduinoMega laying araound, and test showed, original driver is working as expected on ArduinoMega

If you want to buy a Teensy go ahead, because it is worth to have one.
But as I know Teensy 3.5/3.6 is on the way (kickstarter.com)

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