I tested the EditItemTemplate live demo by attaching a RequiredFieldValidator to RadEditor placed in the EditItemTemplate and I was unable to replicate such a problem as you can see in this video: http://screencast.com/t/bDRCvmvufZff.
We are about to release today Q3 2012 SP1 and my suggestion is to test it once it becomes available for download.
All the best,
the Telerik team
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