strange GDK_NO_EXPOSE events being sent to tooltips

[Vadim Zeitlin <zeitlin dptmaths ens-cachan fr>]

 Hello,

 I have a problem with the toolbat tooltips in my program: they
ar never shown. After some reading of GTK+ sources and debugging
I realized that it happens because gtk_tooltips_event_handler()
receives a GDK_NO_EXPOSE event immediately after GDK_ENTER_NOTIFY
one and so it removes the timeout (just set for 500ms) from the
timeout list and it never expires.

 Of course, running testgtk under gdb I see that this event never
arrives to tooltips_event_handler() in this case, so I wonder what
could I have done to cause it? My code is a bit too big to post it
here, but I do nothing more exotic than

  toolbar = gtk_toolbar_new(GTK_ORIENTATION_HORIZONTAL, GTK_TOOLBAR_ICONS);
  item = gtk_toolbar_append_element(toolbar, GTK_TOOLBAR_CHILD_BUTTON, ...);
  ...          

 Even more strange is that if I change GTK_TOOLBAR_ICONS to TEXT the
tooltips appear (but not if I use BOTH)! I really can't understand what
does this change...

 Thanks a lot for any suggestions!
VZ