tap key (or SpaceFn) function doesn't work out as expected

[wytalfred]

I set my Space key as a dual role key: tap as space and hold as layer switch.
I want this key to work just like that, no matter how many times or how fast I use this key.
As for this code, if I tap and then press space key very quickly and then hold it, it becomes a repeated space key, not layer switch key as expected.