Thanks Brook. I went through the steps above; reverting back to the 2013 default theme, the issue is cropping up only when the W3 Total Cache (http://www.w3-edge.com/wp-plugins/w3-total-cache/) plugin is active. I don’t have any theme overrides in place, so it seems this plugin is the culprit.
I can live with having the plugin deactivated for the time being, but would really appreciate some guidance on resolution here since this is a very commonly used optimization plugin.