Various changes in templates won't take any effect

I’m customizing a template (“Terminal”) and tried replacing a background image of a section, and removing a text shadow. On the UI level everything seems to work fine (preview thumbnail of the new image is displayed correctly, text shadow appears to be deleted), it just doesn’t take any effect in the main window or site preview. Even when I delete the original image in the asset manager it remains displayed. It was replaced properly only when I restarted the designer.

I’ve tried replacing images in another template (“Propel”), same issue. Am I possibly overlooking something?