I just had this issue too. We use an F5 load balancer to handle the SSL so when the websites get the request, it is no longer SSL. Our code can tell it was an SSL request by looking at an HTTP header set by the F5.
It would be nice to use this flag to tell the Telerik Script/StyleSheet Regestrars to use the SSL domains. We are using MVC extensions.
For a workaround for now (not requiring rebuilding the source), on the page that uses SSL, I used HttpWatch to see which scripts and css files were being pulled in with http instead of https and created a telerik.js and telerik.css file containing the contents of the files combined. I then added this to the script/stylesheet manager statements (.css shown, similar for .js):
.DefaultGroup(group => group
This is not optimal but will work for now. One other thing, there is a sprite.png that also needs to be in the local project with edits to the .css to reference the png.
What I would like is to have a new property to allow setting and passing the flag like .DefaultGroup().IsSecureConnection(variable). Of course this would be adding the option to the source code and updates to all references that use the current IsSecureConnection.