Hi David, yup Burr has described that well - selecting edges is a bit different than selecting a "standalone" curve. To select an edge you first do one click on it to select the "whole object" and then a second click will drill in to select either edge or face sub-objects.

That gives you a method to control selecting either an entire solid (with just the first click) or also going in and selecting sub-object pieces with the secondary clicks.

Check out here for some description of how selection works:
http://moi3d.com/2.0/docs/moi_introduction.htm#selection

- Michael