There is at least one case where the nick whois tooltips (in the text area) don't disappear.

Steps to reproduce:
1. Place a window over the xchat-gnome main window, in such a way that a
   nick of the text area is half-hidden by the window.
2. Put your mouse over this nick, until the tooltip shows up.
3. Move your mouse away from the nick, on the other window.

The tooltip will never disappear, unless you hover the xchat main window again.

Expected behaviour:
I would expect the tooltop to disappear immediatly when hovering another window, like the usual tooltips (like the ones from toolbars) do.