When the StripFormattingOptions is set to "NoneSupressCleanMessage", RadEditor does not take any action of stripping the formatting of the pasted content from the clipboard. You can find more information at RadEditor and the Browser Clipboard
It looks like the pasted content contain something that breaks the cleanUp functionality in your version of RadEditor. If this is an important feature for you, my advice is to migrate to the latest R1 2018 version (2019.3.910) and test it.
If the problem still persists, please open a support ticket and provide steps along with content to replicate the issue on our end. Thank you!
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