Disabling icon disc in ThemeRoller impacts checkbox default state

[dpolivy]

Not sure if this is a ThemeRoller bug, but it definitely makes it very easy to repro. I think this has to do with how the styles are re-used across elements. Basically, if you disable the icon disc background in ThemeRoller, then the "empty" checkbox background never shows up in checkbox widgets.

JSBin repro:
http://jsbin.com/ajInOVEv/2/edit

1. Go to ThemeRoller
2. Under Global -> Icon -> Default Icon, change the second dropdown to be "W/O disc".
3. That sets the background-color: transparent; style for the .ui-btn-icon-*:after classes, which is apparently what's used to render the checkbox icon background in the "unchecked" state.

Seems like this needs to be its own style?