Glider navigation glitch?

I tried using the css class as navigation, I inserted glider-control-1, glider-control-2,… in classes for text widgets to navigate between the slides:

everything works except going back from slide 2 to slide 1, whatever (logical) class I insert: glider-control-1 or glider-control-0, it does not work.
For all other navigation I have to consider the first slide as 0, so from slide 1 to 2 I use glider-control-1 from 2 to 3 is use glider-control-2,…
But as said from 2 back to one does not work, with any class.

Any suggestion on how to fix it?