Since it appears in the center of the screen for 2-3 seconds before the page layout is completed, it will trigger the pop over and not go away when the loading finishes as the mouse is still over the bubbles.
This issue able to be raised with the advertisers at all? Is annoying somewhat to have to move the mouse out of the way and back again to get rid of it.
It must be the page takes some time to render on his PC - slow ISP? The ad is shown on the middle of the page for a split second (in his case it seems longer) and obviously seems to trigger the bubbles coming up.
It doesn't happen to me - when I have ads showing on the pages it's too fast to trigger it...