I played around a bit, and I noticed some additional things:
I can't open Ekiga's address book more than once, when I click the
menuitem a second time (after having closed the address book) nothing
happens. The console says:
(ekiga:11882): GLib-GObject-WARNING **: invalid unclassed pointer in
cast to `GtkWidget'
(ekiga:11882): Gtk-CRITICAL **: gtk_widget_show_all: assertion
`GTK_IS_WIDGET (widget)' failed
After I restart Ekiga it works again, but again, only once.
Let me know if you need some additional debug output.