UPDATE: Ok now that I've seen some "in action". I really recommend to go for a fixed area for the tool tip texts! The user sees its getting more and more (and probably will actually wait for all of it to load -- check this!). Or tries to already click on a label. Then somewhere opens a fixed location with the text. User reads it, when she's done looking back to the dynamic section for an other label, clicks it again, reads the next text and so on. Important is to make clear which labels she already viewed (just like with visited links).
Sorry if I can't provide any studies or so, this is just a solution suggestion and you need to proof the experience with a prototype! One thing to observe would be as I've already said: Do they actually click on anything as long as it still loading? (There is a x of y count that continously counts up so users would probably not even think about already clicking on something)
One solution might be to place the tooltip in a fixed area instead of right next to the entry. Since you have a visual cue that this is the selected one, it might work without being visually directly connected.
An other solution might be a kind of "Refresh"-Button, so the dynamic load is being hidden from the user. But I don't prefer this solution because of the technical cognitive model that you apply on the user through this kind of interface. Your users shouldn't be aware of things like data retrieving. The app should just work.
An other way to think about it: Is the dynamic loading really necessary? Can't you just let them wait for a sec longer?