The fix is in an internal build. You need to download it yourself now or wait until the next update to receive it. Don't worry, it is easy to get the internal build. Take the following steps:
Go to your account
on Telerik.com and sign in.
Navigate to your products page
and select RadControls for Windows Phone.
Look to the right and click the button "Download: Installer and other resources
Now locate the "latest Internal builds" section (see attached image) and click on the hotfix file. Run that file and you'll have the latest version on your machine.