If the spline is not selected, no change.

If the spline is selected:

Incoming Spline !Cyclic && !Keep Shape !Cyclic && Keep Shape Cyclic && !Keep Shape Cyclic && Keep Shape
Non-Cyclic Non-Cyclic (no change) Non-Cyclic (no change) Cyclic Non-Cyclic w/ Extra Point
Cyclic Non-Cyclic Non-Cyclic Cyclic (no change) Non-Cyclic w/ Extra Point

@jacqueslucke expected behavior

Incoming Spline !Cyclic && !Keep Shape !Cyclic && Keep Shape Cyclic && !Keep Shape Cyclic && Keep Shape
Non-Cyclic Non-Cyclic (no change) Non-Cyclic (no change) Cyclic Cyclic
Cyclic Non-Cyclic Non-Cyclic + Extra Point Cyclic (no change) Cyclic (no change)