When a SingleClick RadButton is clicked and its AutoPostBack property is set to false its disabled state as well as the optional text from the SingleClickText property are persisted. For the time being the SingleClick functionality can be set on the client. For example:
ASPX:
		<script type="text/javascript">
			function DoSubscriptionValidation(button, args) {
				var isPostBack = window.confirm("Perform postback?");
				button.set_autoPostBack(isPostBack);
				if (isPostBack) {
					button.set_singleClick(true);
					button.set_singleClickText("Please Wait");
					button.click();
				}
			}
		</script>
		<telerik:RadButton ID="RadButton1" runat="server" Text="Click"
			OnClick="OnClick1" OnClientClicking="DoSubscriptionValidation" />
C#:
	protected void OnClick1(object sender, EventArgs e)
	{
		System.Threading.Thread.Sleep(2000);
	}