hi, erzane:
I think in your last image above, you did not include that remnant in your selection before moving the selection. Maybe not. But it kind of illustrates the good practice of making a component as soon as you have constructed an assemblage of unique geometry. You do not have to give the component a unique name right away, if it interferes with your workflow, but is good to go back and name it, even set up layers to place these components. After all the time I have been using Sketchup(a few years), this is finally sinking in to my thick head.