AutoCompleteExtender empty list vertical line anomally

I have two (2) functioning AutoCompleteExtender's on my page. One is servicing a GridView inside a FormView. The other is inside the same FormView, but inside a TabPanel. Like I said, both work, but the one inside the TabPanel displays this vertical line that appers to be the outline of empy result listing.

When I click inside the TextBox and begin to type and receive results it goes away or is transformed into a populated result listing.

Here is the markup.....

<asp:FormView ID="FormView2" runat="server" Width="100%" DataSourceID="SqlDataSource2" DataKeyNames="ISTM_NMBR, CKIN_DATE" ><EditItemTemplate><asp:Panel ID="Panel_EditItemTemplate_Details" runat="server" Width="100%"><table cellpadding="3px 5px 3px 5px" style="border-collapse:collapse;"><tr><td valign="top" align="right"><asp:Label ID="Label7" runat="server" Text="Machine:" ></asp:Label></td><td valign="top" align="left" colspan="3" ><asp:TextBox ID="TextBox_MACHINE" runat="server" Text='<%# Eval("MACHINE") %>'
					CssClass="textbox_watermark_footer" /><asp:AutoCompleteExtender runat="server"
					ID="AutoCompleteExtender2"
					TargetControlID="TextBox_MACHINE"
					ServiceMethod="GetActiveMachines"
					ServicePath="~/Shared/WebService/Machines.asmx"
					MinimumPrefixLength="1"
					CompletionInterval="1000"
					EnableCaching="true"
					CompletionSetCount="20"
					ShowOnlyCurrentWordInCompletionListItem="true"
					DelimiterCharacters=";,:"
					UseContextKey="true" OnClientPopulated="onListPopulated_MACHINE"
					BehaviorID="AutoCompleteEx_MACHINE"
					CompletionListCssClass="CompletionList"
					CompletionListHighlightedItemCssClass="CompletionListHighlightedItem"
					CompletionListItemCssClass="CompletionListItem"></asp:AutoCompleteExtender></td></tr>

....and CSS

.CompletionList
{
    border: solid 1px #444;
    margin: 0;
    padding: 2px;
    height: 150px;
    overflow: auto;
    background-color: #666;
    font-size: .85em;
    text-align: left;
}
.CompletionListItem
{
    color: #ccc;
}
.CompletionListHighlightedItem
{
    background-color: #ffc0c0;
    color: #000;
    cursor: default;
}

JS function

function onListPopulated_MACHINE(sender) {
            var completionList = $find("AutoCompleteEx_MACHINE").get_completionList();
            completionList.style.width = 'auto';
        }

Nothing out of the ordinary.

I hope that someone can offer a solution.

Thanks.