Jumbled dashboard after switching from 1-column to 2-column layout

A client of mine switched the screen in his edit pages to 1-column, then back to 2-columns. However, the screen now appears jumbled for him.

Instead of a clean 2-column layout, the right column boxes are sitting on top of the edges of the text editor and other boxes, preventing him from seeing what he’s doing as he types.

Anyone having trouble like this? I’m able to switch back and forth between the two formats seamlessly, so I don’t know what to tell him. He is using the latest version of wp.