GtkTreeView: Green rectangle on drag below tree area in GNOME
evolution-3.50.1-1.fc39.x86_64 on Wayland:
When the folder tree pane is not entirely covered by folders and there is some free space at the bottom, selecting a message in the message list pane and dragging it to another folder in the folder tree pane does not only render a box around the folder below the mouse pointer but also renders a box in the free space below all folders in the folder tree pane.