Hello! Thank you in advance for reading. Posting this as suggested by a support agent in both Bug Report & App Feedback:
I had a person on my friend’s list who I blocked. This removed them from my friend’s list and closed our chat window in my Social tab of the BNet app. However, it did not close our chat window in their Social tab of the BNet app. They can use that fact to see my online/in-game status and potentially use that information (tested this with a friend).
This might seem innocuous but from my experience it has brought a lot of stress and harm. I don’t think blocked parties on BNet should be able to view the online/in-game status of the blocker (and it should just show the blocker as offline or take away the status circle entirely).