Edit: Yup. Confirmed, 4 repeats: open Km forums, then Weatherzone, tooltips say open. Open Weatherzone w/o KM forums, tooltips shy.
Actually, "Open any website, then Weatherzone, tooltips stay open".
I'm inclined to think it's a site problem. Maybe. IE doesn't do it, Opera 9.51 (Presto, now not on this machine) didn't do it. I don't have any other browsers to test against yet.