I seem to recall there was a plugin that commandeered the Undo function somehow. I'm thinking it was an older version of Jiminy-Billy-Bob's Layers Panel. If you've got it and haven't updated it, try that. As for your rendering issues, what rendering application are you referring to? You refer to reflections so that can't be native SketchUp.

You do not "select" them. Endpoints are the only entities in SU that are impossible to "pre"-select BUT they can be "auto"-selected by the Move tool. Just hover over the endpoint until you see the green "Endpoint" tooltip and click to start moving it. (Awful music)