I understand that position for Alert Notifications, since they are for that purpose. But, I consider Broadcast Message as a method for sending a regular message to multiple users. They CAN (and do) respond to these messages, and those responses come into chat history, but there is no record of what was sent to them that spawned the new discussion. That is why I would consider it a bug.
I have not used other clients that have the broadcast functionality, so I can’t comment on how those are handled. I believe that if a user has not disabled history, then they wish to log every message that goes in and out of their client.