There is a option in the config file called "sidedef_add_del_buttons" setting it to 1 (by editing the config file) will restore those buttons.
That's satisfactory for me. I accept it's a bit of an expert-user "here be dragons" feature. Thanks, -- ⢀⣴⠾⠻⢶⣦⠀ ⣾⠁⢠⠒⠀⣿⡁ Jonathan Dowland ⢿⡄⠘⠷⠚⠋⠀ https://jmtd.net ⠈⠳⣄