Ajax Control toolkit ComboBox MaxDropDownItems setting has no effect

I am attempting to limit the number of visible list items in an Ajax ComboBox control.  I thought the MaxDropDownItems property was supposed to accomplish this for me but has no effect on the control when rendered in a browser.  The following code snippet shows the properties I have defined for the control:

<ajaxToolkit:ComboBox ID="ComboBox1" runat="server"

              DataSourceID="SqlDataSource1"

              DataTextField="FullName"

              DataValueField="Record_ID#"

              OnSelectedIndexChanged="ComboBox1_SelectedIndexChanged"

              AutoCompleteMode="Suggest"

              AutoPostBack="True"

              ClientIDMode="Static"

              Height="22px"

              TabIndex="1"

              MaxDropDownItems="5">

</ajaxToolkit:ComboBox>

It does not seem to matter what what value I use for the MaxDropDownItems property.  There is no effect on the rendered control. 

Suggestions would be greatly appreciated.