I believe you have formatter reordering turned on (JustCode Options - Code Style - C# - Ordering - Reorder code elements when formatting) and you do formatting with the cleaner. We have some problems with determining which comment to which construct belongs. In that case we don't move the documentation with the member. This is a known issue and we will fix it.
Sorry for the inconvenience!
All the best,
the Telerik team
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