I guess for another example, when I mark a message as unread on Discord, it doesn’t immediately whisk me away – it moves the ‘read’ indicator back up and maintains it after I leave to go to another channel. It will stay unread until I come back to the channel and read the messages.
Maybe it’s a bit different with topics though – I don’t use this feature very much at all in Discourse, so I can’t really say what expectations / preferences would be most helpful for me.