The problem that you have encountered is really strange. We haven't changed the behavior of the installation packages for any of the DevTools in terms of Toolbox registration. This means that Toolbox items should be registered by the latest install the same way they were registered by older versions.
Can you try to reset the Toolbox after installing the latest version if the Toolbox items are still missing? While installing the RadControls can you make sure that all Visual Studio instances are closed?
While testing in our test environment we haven't encountered any problems regarding Toolbox registration of the latest version.
I hope the information provided will help you.
the Telerik team