Campaigns Preview does not display columns

Campaigns Preview does not display columns

I've created a template using a header image, columns, and a footer image. The columns are set at 70:30. The first two times I previewed the template, the preview displayed the columns properly. 

In subsequent previews, the column formatting is not displayed. The left-hand column (70%) displays across the entire width, with the right hand column displayed beneath it. The columns structure appears properly in edit mode. 

I've created a second template with the same structure and I'm getting the same result in the preview (losing the column formatting).