Preview Pane Displaying as Mobile on Desktop

[TexasGreg]

This is a minor issue but in the preview pane an email shows as if it is detecting a mobile device even though I'm using a desktop using the entire width of the screen. If I put the view source code of the email in an html file it displays correctly in a browser window by itself. Is there a setting I haven't found? I tried upgrading to 1.3.1 but it didn't change. Thanks