This is similar to ICE-5607:

http://jira.icefaces.org/browse/ICE-5607

The panelTooltip is displayed far from where the hover occurs (much lower than expected, nearly off the browser viewing area) when one hovers over the panelGroup element that is defined for the panel tooltip. In my case, I'm using the tooltip component within a datatable which is contained within a portlet. Here's a snippet of the markup:

<ice:dataTable value="#{pooledItemList}" var="task">
<ice:column>
<ice:panelGroup panelTooltip="descriptionItemPanelToolTip">
<ice:panelTooltip id="descriptionItemPanelToolTip" hideOn="mousedown" hoverDelay="500">
...

I looked at tooltip_panelpopup.js and traced it down to the following line (revision 26133) in adjustPosition:

if (y - elementDimensions.height - tooltipOffset < viewportScrollOffsets.top) {
       //align tooltip's top edge with the top edge of the view port
       element.style.top = (y + viewportScrollOffsets.top - elementOffsets.top) + 'px';
}

I was getting the following values for the above properties:
y: 317
elementDimensions.height: 544
tooltipOffset: 4
viewportScrollOffsets.top: 0
viewportScrollOffsets.tip: 0
elementOffsets.top: -231

The offending property value seems to be the value for elementOffsets.top. Seems like we shouldn't subtract the elementOffsets.top value in the calculation for the element top value (since the offset will typically be negative? Not very familiar with JQuery). Unfortunately, I still don't think I fully comprehend the entire context of the calculation, so I may be wrong here. But my fix just involved changing the subtraction to an addition:

if (y - elementDimensions.height - tooltipOffset < viewportScrollOffsets.top) {
       //align tooltip's top edge with the top edge of the view port
       element.style.top = (y + viewportScrollOffsets.top + elementOffsets.top) + 'px';
}

After that change was made, the y positioning of the popup was correct. Again, I'm not entirely sure if this is the correct fix though, but it does seem to work.