DrDiettrich:
Things are not so clear if you use attach/detachInterrupt()I'd only attach the interrupt once, and never detach it. For deactivation use a global flag, that can be tested in the handler.
Before I asked my question here on this forum I have tried all combinations. Also to use attachInterrupt() only and not detaching. However the result is the same - get the interrupt twice.
And I am really puzzled and curious how to solve this.