1. Does the formatting gets cleared if you switch between Design and HTML tabs? Could you try to reproduce the issue on Sitefinity's demo
2. Check [sf_CmsTextContent] table to see the actual content that goes to the database - this is if you use shared content. If the content is not shared check [sf_CmsControlProperty] where Name='content'
RadEditor control does not support highlighter and code validation out of the box. You need to create a custom tool which gets the RadEditor.Content and parse it or pass its content to an external validator from where you can receive a response whether your HTML is valid or not. The same apply for the highlighting
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