In GTK+ tooltips are associated to a widget, if the mouse is moved inside the widget area, the tooltip position doesn't change even if the tooltip text changes. To support multiple tooltips for the same widget, we need to set the area of the widget for every tooltip. See bug #49498 that fixed this problem for WebKit1.
Created attachment 163807 [details]
Thanks for the patch. If this patch contains new public API please make sure it follows the guidelines for new WebKit2 GTK+ API. See http://trac.webkit.org/wiki/WebKitGTK/AddingNewWebKit2API
Committed r128871: <http://trac.webkit.org/changeset/128871>