About once a month I find myself with a chat-window link tooltip that
has somehow outlived the chat window that spawned it.
This could be <http://bugzilla.gnome.org/show_bug.cgi?id=46741>, but
the remedy suggested there -- to return the pointer to the window that
spawned the tooltip -- is not possible in my case because the chat
window is already closed. The only way I can get rid of the tooltip is
to quit Pidgin.
I have not found a way to intentionally reproduce the situation, and I
can't say for sure whether I closed the chat window with Ctrl+W, or
via the window manager's decoration, or what.