Why does a single line span yield a taller button?

[DARK987]

So I'm trying to make some fancy radio buttons and I'm getting some weird effects. I'd like to make them all uniform is size, but I'm getting a different size dependent on whether or not the span is one or two lines. I can "hack" it to fix it by adding \[code\]<br>&nbsp;\[/code\] to the end of the button names for single liners, but that seems particularly inelegant.Note that I've stripped the JS out since at this point the issue is with the CSS.http://jsfiddle.net/aslum/BMbN2/2/