[Gtk-sharp-list] Strange bug

[fmoraes@nc.rr.com]

This seems to occur on with my dialog (has a TreeView with a custom ListStore model). It works fine for the first instance of the dialog. After I close and destroy it, I reopen, remove an item from the list and try to append a new one and I get the exception below:

Unhandled Exception: System.NullReferenceException: Object reference not set to
an instance of an object.
   at Gtk.ListStore.gtk_list_store_append(IntPtr raw, TreeIter& iter)
   at Gtk.ListStore.Append()

Any ideas? This is with GTK# 1.92.

Francisco