Interesting... I'm running xp x64 and don't think there's a sp3 for it, though I keep it up-to-date.
However, I just looked at possible tooltip problems and noticed if I placed the cursor over a node group name or individual object name, I see a quick flash -- too quick to read the text, but over a node input/output/menu item/menu button I see the correct tooltip. Moving the cursor in the preview also sometimes shows the flashing textbox -- not sure if it's supposed to display an object name?
Is this related?