We had the following problems when a RadDropDownList has properties set to:
<telerik:RadComboBox runat="server" ID="cmbStation" Width="100%" AutoPostBack="true" CausesValidation="false" EmptyMessage="Choose one" MarkFirstMatch="true" DataSource='<%# Stations %>' />
Once we clicked "clear" the content of the RadComboBox with the "X" button in IE or clear manually, no postback was raised from the control.
Instead have a "telerik" way, we just set the client event "OnClientDropDownClosing" the following javascript fonction:
function CheckIfCleared(sender, eventArgs) { if (sender._value == "" && sender._filterText == "") { sender.clearSelection(); sender._applyEmptyMessage(); __doPostBack(sender._uniqueId, 'SelectedIndexChanged'); } return true;}