We are aware of a problem when one of the page is under HTTP and the other one - under HTTPS. However, this problem causes a permission error. This problem is not directly related to the RadWindow but to security mechanisms and how the browsers work. If e.g your main page is under http while the page loaded in the RadWindow is under https and the different protocols are treated as if they were different domains. This is called cross domain scripting and it is a security feature in browsers so there isn't a way to disable it. This being said you cannot manipulate the RadWindow's content page if you do not have both the pages in the same domain and under the same protocol. More information can be found in the net, e.g the following search:
The RadWindow is actually an IFRAME which is on the main page and it is not another window object - as a result you have one main page and an IFRAME with another page loaded in it. When you close the RadWindow you hide the IFRAME and this IFRAME always resides on the same main page - thus even if you close it from inside the content page, "closing" it means that you manipulate the IFRAME which is on the main page. This is how the things work and you can test with a standard IFRAME as well - the result will be the same.
This cannot be workarounded and even if this was possible, it would lead to very big risk of hacker attacks.
If this is not the case, please provide a live url along with detailed reproduction steps and we will examine it and we will do our best to help.
All the best,
the Telerik team