Especially on Special:CX, where page layout changes soon after load
(for example scrollbars get added when more content loads), the tooltip
would be positioned incorrectly. Now it is more likely to be positioned
correctly, and will get re-positioned again if it is shown again after
being hidden.
Bug: T145483
Change-Id: I527fc62b196e55101950cffcc6ec43926f63aa4a