Currently if the MinValue or MaxValue properties are changed on the client, on the server the numeric value is auto-corrected according to the their old value.

Disabling the ViewState can help. Here is a basic example that can be used:

		<telerik:RadNumericTextBox runat="server" ID="rtb1" EnableViewState="false"></telerik:RadNumericTextBox>
		<asp:Button ID="Button1" Text="1 change max value and value with JS" OnClientClick="changeValues(); return false;" runat="server" />
		<asp:Button ID="Button2" Text="2 postback" OnClick="Button2_Click" runat="server" />
		<script>
			function changeValues() {
				var rtb = $find("<%=rtb1.ClientID%>");
				rtb.set_maxValue(100);
				rtb.set_value(100);
			}
		</script>

	protected void Page_Load(object sender, EventArgs e)
	{
		if (!Page.IsPostBack)
		{
			rtb1.MaxValue = 20;
			rtb1.Value = 1;
		}
	}
	protected void Button2_Click(object sender, EventArgs e)
	{
		Response.Write(string.Format("currValue: {0}<br/> maxValue: {1}", rtb1.Value, rtb1.MaxValue));
	}