Resizing worked by snapping the the character cells, avoiding unnecessary blank space on the right hand side and bottom of the window. With the deprecation of gtk_window_resize_to_geometry() in GTK+ 3.20 which is a noop now, this behaviour has changed and resize works on a pixel-base. GTK+ docs suggest applications should do the calculactions done by gtk_window_resize_to_geometry() on their own and so should gnome-terminal.