I was not able to reproduce the behavior that you described using the normal WPF Telerik binaries. However, please note that if you're using the NoXaml version of our assemblies, you will have to manually add styles and ControlTemplates for the RadCartasianChart. Please examine the Setting a Theme (Using Implicit Styles)
tutorial for more information on the matter.
Also for your convenience I attached a sample project using the XAML definitions you provided us with.
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