We upgraded out radcombobox component to the latest version (2012.2.724.40) today from version 2009.3.1314.20. Previously when we pressed tab the selected item was selected when we pressed tab, now it only works when we press enter. We didn't change any of the code, and we didn't use any javascript to accomplish this behavior.
<telerik:RadComboBox ID="ddlLevel1" runat="server" EnableEmbeddedSkins="false" skin="ourSkin" style="float:left;padding-right:1px;" Filter="Contains" AllowCustomText="false" MarkFirstMatch="true" IsCaseSensitive="false" AutoPostBack="true" Width="126" OnClientFocus="OnClientDropdownFocus" SelectOnTab="true" />