If setting category style is none the sidebar is showing color boxes on category section.
I know. This is really minor one, and perhaps more styling question than a real bug — but because expectation is even the sidebar would follow forumwide settings this is a bug.
you fix is good first aid tip, until someone codes categories section of sidebar better, and because it is far away from top list of important things todo, that CSS snippet could be the working solution too
Our long term plan here is to completely drop the category style site setting and offer theme components instead for people who want to play with styles.
style box in sidebar would be extremely oppressive in sidebar for example.