See http://www.telerik.com/community/forums/aspnet-ajax/tooltip/changing-targetcontrol-on-the-client.aspx
It should be expected that this timeout around the public API is not needed and the problem is taken care of internally by the control.

When the tooltip is behind the modality it cannot be closed by the users. 

You can workaround this behavior by following the script below:

<telerik:RadButton runat="server" ID="RadButton1" Text="Hover"></telerik:RadButton>

<telerik:RadToolTip ID="rttAdditionalFeatures" runat="server" ManualClose="True" Modal="True"
    TargetControlID="RadButton1" ShowEvent="OnMouseOver" OnClientShow="OnClientShow">
    Some text
</telerik:RadToolTip>

<script type="text/javascript">
    function OnClientShow(sender, args) {
        var modalLayerZindex = sender._modalExtender._backgroundElement.style.zIndex;

        if (sender.get_zIndex() <= modalLayerZindex) {
            sender.get_popupElement().style.zIndex = modalLayerZindex + 1;
        }
    }
</script> 

A workaround is to force the tooltip to update its position when the content arrives (i.e., in the OnClientResponseEnd event: http://www.telerik.com/help/aspnet-ajax/tooltipmanager-client-side-on-response-end.html )

function OnClientResponseEnd(sender, args) {
    var activeTooltip = Telerik.Web.UI.RadToolTip.getCurrent();
    if (activeTooltip) {
        activeTooltip.updateLocation();
    }
}

When the following properties are set - HideEvent="LeaveToolTip" and RenderMode="LightWeight" and the mouse cursor is moved over the ToolTip in a slower motion, the tooltip itself is hidden.

The error that is thrown on page load is that two components with the same ID cannot be added to the page.

Possible workarounds:
1) set EnableAriaSupport to false
2) use client-side code to show tooltips, as shown in this demo: http://demos.telerik.com/aspnet-ajax/tooltip/examples/radtooltipmanagerclientapi/defaultcs.aspx .

A possible workaround is to add the background-color via CSS:
		div.RadToolTip.RadToolTip_Office2007,
		.RadToolTip_Office2007 div.rtContent
		{
			background-color: #d7e3f2;
		}

The request needs to be encoded for the WCF service context to be able to recognize the data as a class the developer can create.
A small sample is attached that:
- overrides a function from RadToolTipManager to encode the request
- has a simple WCF service implemented that shows how to access the passed data and use it

The workaround is to avoid the other settings (e.g., Auto). In most cases Lightweight RenderMode will suffice, the only potential issue is loss of gradients, shadows and rounded corners in IE6-8.

Telerik version - 2011.1.614.35

RadToolTip issue seen on Chrome (version 28.0.1500.95) and Safari (version 5.1.7)

The RadToolTip doesn’t align properly with the control that was hidden initially.
i.  There is a label control inside the RadGrid header template, that has RadToolTip attached.
ii.  On page load, the column is hidden.
iii.  The column is made visible when a particular button is clicked (client side event).
iv.  When the cursor is hovered over this column for the first time, the tool tip is seen at a distant place away from the label.
v.  However, when hovered again, it is seen properly aligned with the label control

When the page is in RTL mode and the manual close button of the RadToolTip is hovered it changes its position slightly.