Workaround: 

function OnClientLoad(sender, args) {
    sender._isEditableElementInTemplate = function (target) {

        return target && $(target).closest(".rtTemplate").length > 0 &&
                (target.tagName.toUpperCase() == 'INPUT' ||
                target.tagName.toUpperCase() == 'TEXTAREA' ||
                (target.isContentEditable));
    }
}

<telerik:RadTreeView OnClientLoad="OnClientLoad" ID="RadTreeView1" runat="server" ... >