The thread is about how the "Mark" icon used to work and how it works now. It used to make the selected mails "Read/Unread" and now in Supernova it opens a drop down. Currently there is now workaround for that.
It's the first thing that hit me after upgrading to Supernova. It's annoying to have to reach for the keyboard and press M or waste an extra click to open the drop-down.
