I upgraded to 2.30.2, from 2.29.x. If I now right-click on a folder and select "Mark as read" I am prompted with a dialog with the question "Also mark messages in subfolders?". I have the options "Cancel",  "In Current Folder and Subfolders", and "In Current Folder Only".

This question also pops up when the folder does not have subfolders. It should not! If there are no subfolders, there's no need to introduce an annoying dialogue. 

Also, from a usability point of view, it is annoying to have a pop up box that you have to navigate to, in order to mark the messages read. It would be much nicer if there are two options in the context menu when you click on a folder, one for marking the current folder as read and one for marking all subfolders as read as well.