Hi John,
Yes, this is a known problem. It happens on all platforms. Note that the tool tip windows are truncated only when they are shown from combo boxes or list boxes (drop-down lists that are shown when you click them). Tool tips are shown correctly for the rest of controls.
Normally, the same tool tip is available for both the list box and its corresponding label; place the mouse cursor over the label and you'll read the whole text. Also, the whole text normally appears after some tries for most list boxes.
This is an obscure bug that I am trying to catch for a long time. Sorry for the inconvenience.