I guess it is quite clearly explained that any test that requires moving the mouse
or sending key strokes
requires an unlocked desktop. Telerik tests are not the only types affected by this Windows limitation. You will find this is a general problem with any tool that performs UI testing.
Our tests against HTML-based web applications frequently can work on a locked machine because most test steps don't use the mouse or keyboard. Instead they are able to inject Click or Select events against the element in question (e.g. a button or drop-down select). Unfortunately Silverlight and WPF applications do not allow us to inject these events. We have to simulate system wide mouse moves, clicks, and key presses instead.