This is related to (fallout from) Don't require a click to switch between sites, inbox, and Achievements on the new topbar
Activate the Inbox by clicking on it. Say you wind up clicking more towards the top of the icon than the bottom. Then try to go over to the scroll thumb, or towards the right edge of the first item.
You'll never make it. You get achievements instead, because the straight-line path of the mouse goes over the achievements button:
A couple of ways to fix this:
- If you're moving diagonally from the Inbox icon across the Achievements icon, do not activate Achievements.
- Just put few tens of ms delay between switching. That way, the momentary hovering over Achievements will not activate it.