I’ve done this a couple of dozen times now - replaced the sub’s name with blank.
Seems that I click on the sub already selected (flipping it to rename mode) then press space to go to first unread. Then probably click on the message list since it didn’t work. Single space name accepted 🙂
Would it be sensible to move the function of renaming a sub to a right-click menu option, rather than second click on a selected sub? At least for myself, renaming a sub is something I may do once intentionally, not on a regular basis, so it doesn’t need to be a ‘surface’ ui feature. One click deep would be fine.