Garvin, thanks, that worked, eventually. I'm still puzzled about why the left column wouldn't get highlighted before, but I just moved the plugin around until I saw the border of the left column appear and then dropped it. (I promise I tried that before! In case it would have been useful, I even ...

I am trying to customize the template "Idea" but I can't move any plugins to the left sidebar. The preview screenshot that comes with the template shows it having three columns (left sidebar, middle section, right sidebar), but every time I add a sidebar plugin from the Configure Plugins page, it ...