The 'overflow' style when used with values "scroll | hidden" is incredibly useful in controlling floats and margins on your page. When an element is assigned one of these styles, it becomes "a new block formatting context". What that means is that all interior floats (within that element) are automatically cleared, and no interior margins can escape the container. The problem you were having was that a subsequent element was somehow (and I'm not really sure why - didn't look closely enough to diagnose it) expanded enough vertically to MASK the linked buttons. When the buttons are masked, the mouseovers are not detected by the browser and the links don't work. By assigning the overflow style, you prevent that masking and the links are expressed.
It's definitely a more elegant approach!
