We are not able to open hyperlinks which are in the content area of the RadEditor. We are experiencing this behavior in our code as well as on your demo site. Here is how to replicate the issue on the demo site.
a) Go to the overview page on the RadEditor demo site: http://demos.telerik.com/aspnet-ajax/editor/examples/overview/defaultcs.aspx
b) Clear all content in the RadEditor
c) Click on the <html> tab for the RadEditor
d) Enter the following hyperlink into the content area: <a href="http://www.w3schools.com/html/">Visit our HTML tutorial</a>
e) Click on the Preview tab of the RadEditor
f) Click on the hyperlink for d) above. This will not take the browser to the hyperlink which was added into the content area
This behavior is consistent between Google Chrome, Firefox, Edge, Safari and IE