Indeed, there isn't an event that is fired when the RadWindow loses focus. If you need to look for which RadWindow is active you can attach an OnClientActivate handler for all your RadWindows (e.g. in the manager's markup) and store in a global variable the previously active RadWindow then when the handler is fired - check if this is the same one or a different one, execute your logic on the old variable and store the currently active one. Aleternatively you can use jQuery to add a onmouseout handler to the RadWIndow, raise a flag in it and then use a handler to onmousedown - if the click is not inside RadWIndow and onmouseout has been fired then the radWindow has been deactivated.
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