Hm yeah true I am not getting the mark as read either. Usually mark as ready basically means archiving for me as I would not have to keep it in the inbox.
If I have something else I want to work on for a task I will assign a task or subtask directly to keep the inbox clean.
Asana provides “Archive Notification” (shortcut E, also shows as the archive box icon) command for something that is “Mark as read”. This marks as read and moves the notification to archive.