There is no Undo button at present, so take care.
Once again, there is no Undo button at present, so take care. If you do make a mistake, you can use the Add Point button to amend it.
This tool is intended primarily for marking up an image. If this is the case, the lowest object in the canvas' display list will be the image being marked-up. In the case of *.rppm files, if objects are lowered below the photo-widget, they cannot be seen, so therefore cannot be reselected. For this reason, when objects are lowered, they are lowered to a position above the lowest object.
Gudge.