Seems there have been the occasional bug report throughout the years.
The mount (Z) and hearthstone (B) buttons are unclickable, don’t have tooltips, and cannot be option-clicked to announce the cooldown. The latter is the most important functionality and really hurts when I’m playing global heroes like Dehaka, Falstad, or Brightwing. While there have been earlier reports by other people, I’m reporting this again in the hopes it’ll be fixed after all these years. I really like this game and this is practically my only big issue.