The cause for this was quite simple-- a misplaced bitwise operation
before passing a value to the function that grayed out buttons based on
their state, caused by refactoring in rB933bf62a611f before committing.
What makes the situation a little more confusing is that the theme colors
are overridden for list buttons in UI lists, necessitating a second
call to `ui_widget_color_disabled()`. Ideally that wouldn't be necessary.
61f1faac3f