Thank you for your feedback.
I'm happy to inform you that the issue you noticed has already been fixed. I would suggest to update your version of the VSExtensions to the latest one and give it another try. Please follow these steps:
1. Start Visual Studio.
2. Open the Extensions and Updates manager from the Tools menu.
3. Expand the Updates tab and select the Visual Studio Gallery sub-tab.
4. Select the Telerik WPF VSExtensions and click on the Update button.
5. Follow the installation steps and restart Visual Studio when prompted.