Thank you for the report.
Our common practice as far as new browsers / browser versions are concerned, is to release an update about a week after the official browser release. The reason for this is that beta browser versions have bugs as well as changes that do not make it in the final version and we have had plenty of problems in the past addressing beta issues that fail to occur in the actual official release.
Let us know if you find any other problems concerning RadEditor usage in IE9 beta.
the Telerik team
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