Thank you for the question.
This problem is not related to our component, but it is an issue with Blend. This issue is not present with Windows Phone 8 version of the controls.
You can find the style of the RadToggleSwitch if you decompile
and the style is located in themes/toggleswitch.xaml
in the assembly resources.
I hope this helps. Please, let us know if you have further questions.
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