That is really weird and we are sorry to hear that you have such problems.
Can you please answer the following questions:
1.What is the version of RadControls for WPF you are currently using?
2.With which controls you are experiencing such problems or this is valid for all RadControls?
3.Are these controls rendered correctly at runtime?
4.Are you trying to edit some template and what is the case when you edit the template of particular RadControls.
5.Are you sure that all references you use are with the same version?
You may try to reinstall these controls and add the references you need manually in Expression Blend.
Also verify that you did not have installed any older version of RadControls/WPF.
I will be waiting for your response.
the Telerik team
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