Thanks, Bhagpuss! I think I figured out the ‘problem’ and I posted about it here=> Missing Sidebars – Vexed by responsive design.

Basically, the left and right sidebars on the home page (with the list of posts) are being ‘hidden’ by the responsive site design due to the size of the browser window. I suspect there are some tweaks I can make to the theme settings to make this a little less likely to happen.

This behaviour can be altered by using the browser’s ‘Zoom in’ and ‘Zoom out’ capability i.e.: you you zoom in (making all the page elements larger) the sidebars may be disabled and vice versa.