As you may know Telerik controls in Windows/Windows8Touch theme use resources, which are linked to a one major singleton that contains the colors used in those themes.
Such an approach enhances the customization of a theme in few steps. On the other hand the same approach slows down the performance of virtualized components, such as RadGridView.
By that reason you are not experiencing the same with another theme as you already mentioned.
Would it be possible to share your own project, which we can test by our side?
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