Indeed, the code sample you posted leads to the described problem.
Note that the broken source in the image is reflecting not only the PDF reader, but the Preview and Design mode as well (can be observed in the attached clip). The exporting logic does not implement the functionality for validating HTML code, neither the RadEditor.
As mentioned the data is set from the code-behind and currently I could only make assumptions on why the slashes are inserted. I could suggest you to investigate the implementation responsible for the content and see if there is a logic that could lead to the problematic behavior.
For example you could replace the double quotes with single or using the @
character, so that the escaping for these characters will be avoided if this is the case.
If you are still having difficulties please get back to me with information about the mentioned code-behind implementation or a simple, fully runnable project that shows it
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