icons don't work on input type submit

http://jsfiddle.net/nxatF/

please see the above fiddle or use this code to see the issue:

<input type="submit" id="foo" name="foo" value="foo"/>
<button id="bar">bar</button>
var options={"icons":{"primary":"ui-icon-disk"}};
$('#foo').button(options);
$('#bar').button(options);

the button will have the icon, the input type submit will not