In short - the answer would be "no, this is not a bug", as this is not the intender purpose of the RadEditor.
The browser's Rich Text Editing engine checks for unclosed and non well formed tags and corrects or tries to correct them automatically without providing a way to disable the browser validation. This means that it is not always possible to validate non well formed HTML content.
Please note that RadEditor is not an HTML validator or improvement tool (and neither is the ConvertToXhtml content filter), therefore you should set valid HTML content in it in order to get proper results.
The best solution is, as was proposed in the other thread, to instruct the users to use a validator.
Alternatively you could look into HTML repairing tools and fix the files in your database yourself. Unfortunately we cannot recommend third party software.
the Telerik team
Registration for Q1 2011 What’s New Webinar Week is now open. Mark your calendar for the week starting March 21st and book your seat
for a walk through all the exciting stuff we ship with the new release!