There is a bug with ordinal property. Please excuse us for the inconvenience. As a workaround you can add the custom field trough the configuration(as in the image you provided) by going for example to the Main Section and add a new field of the required type. The field will be added to this section. New sections will always appear under the default ones. You can reorder custom sections in App_Data/Sitefinity/Configuration/NewsConfig.contentViewControls.NewsBackend.views.NewsBackendEdit by changing section order from top to bottom.
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