When using the calendar plugin, this odd “arrow” appears under topics in the category view when you hover your mouse over a topic:
It’s also just a little wonky in the context of the theme in general, but it’s possible this is just my custom theme…
I think it might be an empty one of these: (Discourse Tooltips)
I wouldn’t have guessed that, my bad 
The next time your site is updated those weird houses will be gone!
But where will the calendar gnomes live after then? 
If I had a dollar for every bug I found in Discourse…I’d have a few bucks. But if I had a dollar for every problem Discourse has solved for my community, I’d be set for life!
Thanks for removing the monopoly house from my UI 
