Steps to replicate the issue (include links if applicable):

• Go to your preferences and change the default image size
• Go to an article with some existing images of different sizes (some using |upright=)
• Open VisualEditor and try adding images or modifying existing ones using the VisualEditor dialogue. Switch back and forth between source mode and VisualEditor, perhaps.

What happens?:

The image sizes that are displayed in the VisualEditor preview quite often do not match the size that they render after one hits publish. I'm not sure exactly what step the bug(s) are being introduced in, but they're not hard to come across.

What should have happened instead?:

The images should render in the preview correctly, at the same size they will be after the edit is published.

Other information: See T64671 for a related task.