I already answered your support thread and for your convenience I pasted my reply below:
I created a sample test demo based on the provided description in order to test the described setup but I was not able to reproduce the problem - everything is working as expected and an ajax request instead of a postback is performed. I attached my test demo to the thread - please examine it and in case the problem persists, modify it in order to replicate the problem and send it back to me along with a detailed explanation of the problem and reproduction instructions.
For your convenience in the demo I have two label control - one of them is updated only when a postback occurs and the other one is updated also buy using AJAX. As you can see, when you have configured the RadAjaxManager proxy to update the second label, no postback occurs and the first label does not get updated. If you disable AJAX you will test the behavior in postback scenario - both labels are updated together.
Let me know how it goes.
All the best,
the Telerik team
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