Hello Adrian Pay,
We are aware of this issue and it is already fixed. The fix is included in the 2010.1 603 version of the controls.
I prepared a sample project using the referred dlls. Please take a look at it and let me know if ti works for you.
Also, if you want to reduce the size of your Silverlight application, you should check our latest Silverlight tool online - Assembly Minifier (http://blogs.telerik.com/blogs/posts/10-06-10/telerik_assembly_minifier.aspx
the Telerik team
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