I activate Banner Notification plugins. Here is how to reproduce. 1. On a folder, mark two message as unread, let's say morning and afternoon message. 2. Move your cursor focus on other folder. 3. Click on afternoon message inside Banner Notification (first scrolling message on banner shows latest date, cmiiw). 4. Then both message mark as read. It should be only afternoon message which mark as read. If you mark more then two message as unread, then it will mark the first and the latest as read.