It took me a while to figure out that the z-index for one of the hidden layers I had defined for a yahoo dialog were covering these buttons, making them unclickable in Internet Explorer. In Firefox the z-index was fine. Increasing the default z-index on the layer fixed the problem.
Update: That didn't fix it. I'll have to look in deeper into what is obscuring those buttons.
Update: a dialogs body must be wrapped in a div tag with class='bd'.