There is an error on the page if you scroll before the page is fully loaded:

Uncaught ReferenceError: init is not defined

line 95 of smoothscroll.js.

There is an error on the page if you scroll before the page is fully loaded:

Uncaught ReferenceError: init is not defined

line 95 of smoothscroll.js.

update
Looks like a bug to me try changing:

function ssc_wheel(e) {
    if (!ssc_initdone) {
      init();
    }

to:

function ssc_wheel(e) {
    if (!ssc_initdone) {
      ssc_init();
    }