Edit Page Displays Text in Single Column with Graphene Theme

I use the Graphene Theme version 1.9.3. Suddenly, when editing any page, the text appeared in a single column in the middle of the editor page. The text background was white, the remainder blue. After much experimentation here is what I learned.

The problem disappeared when I switched to another theme, but came back when I returned to Graphene. I was using one main column and one right sidebar. I changed the layout (Graphene Options >> Display >> Column Mode) to a left sidebar. The problem disappeared. I switched back and the problem was still gone.

Apparently upgrading WordPress and/or themes is not quite seamless. Anyway, the problem is gone. I hope this helps someone else.