it shold be:
if ( mynum < 1 ) {
instead
if ( mynum == 0 ) {
That makes the button to go away aven when we are getting out of bounds.
It still sometimes goes out of bounds though, when you boubleclick thumb buttons too fast, also getting a bit choppy scrolling animation when you clicking fast many times in a row, dont know if anything could be done with that, maybe somehow handling doubleclicks ?