There seems to be a problem with inheriting the 19px width that the buttons are given, considering they inherit properties from many different declarations in the CSS file.
Using Opera Dragonfly (like Firebug, or GChrome's Developer Tools), I am able to edit the CSS styling, strangely enough setting a minimum width (of 19px) seemed to work some of the time.
The functionality of the buttons seems to work fine as the links work. Attempting to scroll just creates an even crazier mess.
What I have mentioned about the min-width, may or may not work. All I know is that the display is poor in Opera, even though the correct properties are there (Block, fixed width, no negative margins, etc.)
If it helps, it's the anchor links inside the items container inside the scrollable container.
They are styled by the class PageNav.