I have a MouseOver layer to make some buttons on my site highlight on hover. However, the hover state is also being treated as MouseDown, too, so that when the buttons link to a page on my site, the button is permanently in the hover state whilst the page is displayed.

I'd assumed that a MouseOver layer was just that - it would only be shown during hover - and that to make the effect persist in MouseDown, I'd have to add another layer and duplicate the effect there.

How can I make my site display the hover effect only on MouseOver and not on MouseDown?