I came across an issue with one of our web sites:
In IE9 the page had a vertical scrollbar, but you couldn\'t use the mousewheel, arrow keys, pgup/pgdwn to scroll.
overflow-x: hidden;
would hide any thing on the x-axis that goes outside of the element, so there would be no need for the horizontal scrollbar and it get removed.
overflow-y: hidden;
would hide any thing on the y-axis that goes outside of the element, so there would be no need for the vertical scrollbar and it get removed.
overflow: hidden;
would remove both scrollbars