None of them work for me if clicked twice in a row...
So using one of the three grouped buttons as an example - say the center one (02). Click once and it scrolls down to "Target 2". Now manually scroll back to the top using the scroll bar on the right side of the window. Click (02) again - nothing happens - at least for me.
Ditto all the other buttons. Click on one of them then manually scroll back to the top. Click the same button again - no scrolling. Click another one and everything is fine.
In the actual operation of the page (i.e. not considering the "Smoothly cruise to Target 3" button) when the same button is hit twice in a row it does not show up as a problem because the page has already scrolled to that point. Clicking another button seems to "reset" the previous button's functional operation.
EDIT: A little more research... the "hashchange" event is not triggered when the same button is clicked in succession (or so it appears to me)
From the "jquery.arbitrary-anchor.js" script:
// only scroll to element if href is equal
// to hash; we'll let hashchange event
// handle everything else
if ( href === location.hash )
scrollToHash( href )
// Scroll to the object when hashchange event
// is triggered on the window.