In some cases the result of the cut with knife project is not selected, why? How do I get the result to be selected?
It depends on whether the object you are using as the 'knife' is 'closed' or not. In your first image the circle is a closed loop of edges, so everything inside is selected. In your second image the two edges are not connected so the result of the knife project is not selected.
Closed edges:
Open edges:
If you want the result to be selected then make sure the object you are using as the 'knife' is a closed loop of edges.
I don't 100% understand why this is the case, it could be a technical limitation or done by design.
-
$\begingroup$ Thank you. it should also disable "auto smooth" of the object that will be cut. $\endgroup$ – logiquefloue Sep 20 '16 at 13:28