I'm unsure if this has been discussed as I can't find any bug reports etc. however I think I've found a bug with styling buttons, or more specifically using the button widget to style anchor tags.
The best way to see the bug is to go to the
Button Widget Demo PageAnd in firebug add 'ui-widget-header' to the class attribute of the div tag with class = demo, which encompasses the button elements (screen shot provided)
You'll see that when the button widget styles anchor tags in a widget header the anchor tag's styling is not consistent with the other button types.