What happens if the view direction changes?
Suppose you select the curves, the meshes and the regions to keep. Then you rotate the model with the mouse, which implies a view direction change. In this case, when the Disable Projection check box is cleared, if you click the Update Projection button on top of the selection list ( ), the Regions to Keep selector will be reset, so as to enable you to perform a new selection based on the new view direction.